20 years ago today - May 1994 storm

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20 years ago today - May 1994 storm

Postby wiz » Fri May 23, 2014 4:03 pm

It's hard to believe that the May super storm of 1994 happened 20 years ago today, 23/5/94

Anyone that was in Perth that night will always remember it, here is the headline of The West Australian from the next day

http://members.iinet.net.au/~jacob/94storm.html

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Re: 20 years ago today - May 1994 storm

Postby Blue Skies » Fri May 23, 2014 4:09 pm

Its funny but I remember the aftermath the next day better than the storm itself after all this time, dodging fallen branches on the way to work and having no power most of the day.
2013 rainfall: 910.1mm
August: 138.7 mm to 30th 2014 YTD: 687.7 mm

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Re: 20 years ago today - May 1994 storm

Postby wiz » Fri May 23, 2014 4:15 pm

Blue Skies wrote:Its funny but I remember the aftermath the next day better than the storm itself after all this time, dodging fallen branches on the way to work and having no power most of the day.



Yeah the amount of trees down and big branches was quite amazing. Especially when you drove past any park after that event, it was littered with it.

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Re: 20 years ago today - May 1994 storm

Postby supersmell » Fri May 23, 2014 9:37 pm

yep remember that one! blew like buggery for hours! kids were only little & my old dog got out & took off! kids were bawlin so good ol Dad had to go look for th bloody thing! after nearly gettin hit by a flyin builders dunny thought stuff this & went home,sure enough first thing in the mornin the buggers scratchin on the door! remember th swan bein choppy as hell

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Re: 20 years ago today - May 1994 storm

Postby Fu Manchu » Fri May 23, 2014 10:12 pm

Maybe JR can find some more on the event?
BoM have loads of records on extreme events.
I tried having a dig around but turned up nothing. Couldn't find the page on BoM , but it's there. Found it many times before but not tonight. :(

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Re: 20 years ago today - May 1994 storm

Postby Fu Manchu » Fri May 23, 2014 10:46 pm

I found this. Lowest maximums for the day.
http://www.bom.gov.au/cgi-bin/climate/e ... n=5&day=23

Highest rainfalls for 23 May 1994
http://www.bom.gov.au/cgi-bin/climate/e ... n=5&day=23

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Re: 20 years ago today - May 1994 storm

Postby Fu Manchu » Fri May 23, 2014 11:42 pm

JR the Ferret has ferreted out the synoptic for the event.
Image
Thanks John. You are a lovely bloke.
https://twitter.com/jr_the_ferret/statu ... 6169833475


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Re: 20 years ago today - May 1994 storm

Postby Fu Manchu » Fri May 23, 2014 11:47 pm

The report on the event.
https://dl.dropboxusercontent.com/u/270 ... 201994.doc
Many thanks to JR again ;)

Incase that link stops working

REPORT ON THE SEVERE STORM OF 23/24 MAY 1994
OVER THE SOUTHWEST OF WESTERN AUSTRALIA
L.A. McCready and B.N. Hanstrum
IR Loop

1. INTRODUCTION
On the evening of 23 May 1994, through until the early hours of the following morning, a severe windstorm battered the southwest of Western Australia causing widespread damage, particularly in coastal communities between Mandurah and Geraldton. The strongest sustained winds occurred for a period of about an hour around 2000 WST , but violent squalls in showers continued on throughout the night. The impact of the storm was made more considerable in that it followed a long period of dry stable conditions over much of the southwest of the state.
The windstorm was the most destructive weather event to affect the Perth Metropolitan area in the last 30 years, the total damage bill was greater than 25 million dollars. Several houses were completely unroofed but the majority of property damage was minor, the average insurance claim being $700 and more than 60% of claims were for fence damage. Thousands of trees were either blown down or had large limbs snapped off. Many of these fell across powerlines contributing to widespread blackouts. The number of households affected was so large that power was not fully restored for several days. Examples of the damage caused by the storm can be seen in Fig.1.
Two people on board a yacht sailing from Fremantle to the Cocos Islands were caught in the storm off the coast from Jurien Bay and were lost at sea, presumed drowned. Huge seas and above normal tides caused significant erosion to beaches and parts of the Perth river foreshore were also inundated. Fortunately there were no serious injuries or loss of life on land.
Severe winter gales have been part of the weather history of the region. Periodic accounts of winter storms, from the time of settlement in 1830 through until 1928, are provided in the publication 'Results of Rainfall Observations made in WA, 1929': One of the most severe of these occurred in May 1910 and was reported as follows
Winter conditions set in on the 5th of the month, when an ordinary
winter 'low' passed along the south coast, and fairly heavy rains
fell throughout the greater portion of the state. Thence onwards
till the 27th a succession of depressions passed near the Leeuwin,
and the atmospheric conditions, as a consequence, were of a
persistently unsettled and frequently stormy type. The disturbances
on two occasions were very energetic, a barometric reading of
29.203 inches being recorded at Cape Leeuwin on the 10th. On
this date a terrific gale, accompanied by record high tide and fierce
rain squalls, was experienced at Fremantle. The wind blew from the
northwest with hurricane force all day on the 9th, and, veering to
west-north-west on the next day, increased in violence till a
whole-gale velocity was attained. The seas were very high, and the
waves frequently broke over the north mole, greatly hampering
shipping operations in the harbour. The full force of the gale was
also experienced at Bunbury, where the swimming baths were
completely demolished, and at Cape Leeuwin a wind velocity of
75 miles an hour was registered.
Records from the Fremantle Port Authority(FPA) since 1963 show that severe winter storms have affected the southwest on average about once every five years. Despite these being relatively infrequent, their impact on the southwest region can be considerable and to date no meteorological studies of these events have been published.
This paper firstly documents the data recorded during the May 1994 storm, then provides a reanalysis of the track of the low and an overview of synoptic background to the event. The dynamics of the cyclogenesis that occurred are discussed and an assessment of numerical model performance is provided. A comparison is then made between the May 1994 storm and 4 other events in the past 20 years that produced damaging winds in the southwest of the state. Some implications for forecasting during these events are drawn from this comparison and the final section provides a summary of the paper.
2. DATA
Wind
Power failures affected the availability of data during the event at a number of centres. The highest wind gust recorded during the storm was 143 km/h at Swanbourne automatic weather station (AWS) and much the same at the Fremantle Port Authority tower (height 60 m) assuming a 15 km/h correction due to a faulty pen setting. Other metropolitan recordings included Rottnest Island 133 km/h, Jandakot airport 130 km/h and Perth airport 111 km/h. To the north Geraldton recorded a gust to 128 km/h, the strongest gust for May on record, while in the lower southwest wind gusts recorded were considerably lower. Mandurah recorded 119 km/h, Bunbury Power Station 95 km/h and Albany 93 km/h. Further to the east Jacup AWS registered a gust to 107 km/h and Esperance 130 km/h.
Pressure
The approach of the low was signalled by strong surface pressure falls across the southwest. At Perth the barometer fell 10 hPa in the nine hour period from 0900 WST to 1800 WST on 23 May, when a low of 994.3 hPa was recorded. The lowest pressure recorded over the mainland during the storm was 986.6 hPa at Jacup AWS at 0001 WST 24 May. At Albany the barometer fell to 989.3 hPa at 0001 WST 24 May and at Esperance to 987.7 hPa at 0120 WST 24 May.
Rainfall
Although widespread rain accompanied the passage of the front and low across the southwest rainfall totals were not unusually high. This was attributed to the rapid movement of the system. The isohyetal analysis for the twenty four hours ending 0900 WST 24 May 1994 (Fig. 2) showed a maxima greater than 40 mm over the ranges to the east and southeast of Perth and between Cape Leeuwin and Albany.
Storm Surge
One of the consequences of strong winter storms in Perth, including the 23 May storm, has been the inundation of the river foreshore near the city centre due to higher tides. The tidal elevation measured at the Fremantle Fishing Boat Harbour compared to the predicted tide level (Fig. 3) showed a storm surge of 0.98 occurred at 2034 WST 23 May. The potential for more serious and extensive flooding was not realised in this case as the peak surge occurred near the time of predicted low tide.
Seas and Swell
Two ships located near 30oS 114oE (just off the coast near Jurien Bay) provided information about wind speeds, sea state and swell during the period of the event. At 1400 WST 23 May 1994 seas between 2.5m and 4m and swell between 3m and 4m were being reported. By 0300 WST 24 May 1994 seas had risen to 5-5.5m and the swell had increased to 8-9m. The seas and swell began to ease after 0800 WST 24 May 1994 and were being reported at 2m and 5.5m respectively by 1500 WST 24 May 1994.
3. SYNOPTIC BACKGROUND
Description of Track
Surface synoptic data and satellite imagery at 3 hourly intervals were examined in detail in order to determine the evolution of the low pressure system during the period from 2000 WST 22 May 1994 to 0800 WST 24 May 1994.
The low originated approximately 1000 km to the southwest of Cape Leeuwin and then moved rapidly to the northeast, attaining an average speed of 100 km/h as it approached the southwest coast. The system appeared to become more complex with two lows being analysed, one near Cape Leeuwin and another smaller centre further to the north. The northernmost centre passed just to the south of Perth around 2000 WST 23 May and then commenced a southeast path at a similar speed, crossing the south coast between Albany and Esperance around 0001 WST 24 May. It was during this period that the two lows appeared to consolidate into one main centre which continued to move in a generally south east direction but slowed to an average speed of 74 km/h. The path of the northern low and its estimated central pressures are given in Fig.4.
Deepening of the northern low appears to have commenced at 0800 WST 23 May 1994 and in the following twelve hours the central pressure was estimated to have fallen 8 hPa to 992 hPa by the time it crossed the west coast. This corresponded with the period of the strongest average winds in the Perth area. The most rapid deepening seems to have occurred in the following six hours as the low centre traversed the southwest and merged with the low to the south. The estimated central pressure of the low had dropped to 982 hPa by 0200 WST 24 May 1994.
The presence of two lows, with a col area between them, provides an explanation of why winds around the southwest corner were much lighter than those experienced in the Perth area. During the period when the northern low passed across the southwest, winds at Albany were only of the order of 10 km/h.
The broad scale synoptic setting for the event can be seen from the sequence of RMC Melbourne MSL pressure analyses in Fig.5 a&b and Fig. 5 c&d. Minor modifications have been made to the analyses to incorporate changes to the central pressures and to include the northern low.
Satellite Imagery
The sequence of IR satellite images at 12 hourly intervals for the period 2000 WST 22 May 1994 to 0800 WST 24 May 1994 is shown in Fig.6a and Fig. 6b.
The satellite image for 2000 WST 22 May 1994 (Fig. 6a) showed a cold front lying across the southwest of the state with an associated low well to south of Albany. A field of cold air was visible to the west of the front with a brighter area of cloud between 35oS and 45oS along 98oE.
By 0800 WST 23 May 1994 (Fig. 6b) the leading cold front had moved slowly eastwards. The cloud feature to the southwest had moved rapidly to the northeast around a primary low near 50oS 115oE and had become better organised. Evidence for the existence of the polar front jet can be seen by the sharp transition from the stratiform cloud field to open cellular clouds along 100oE (Guymer, 1978).
During the next 12 hours the structure of the cloud feature took on the appearance of a frontal comma cloud with an extensive cold air field just off the southwest coast. By 0800 WST 24 May 1994 the system had developed into a mature extra-tropical low over the western Bight..
4. DYNAMICS OF CYCLOGENESIS
A study of polar airstream cyclogenesis in the Australian region (Sinclair and Cong, 1992) found that a necessary condition for cyclogenesis in a polar airstream is an upper level south westerly jet streak upwind of the surface disturbance at formation time. They also found that during the initial stages of cyclogenesis the surface vorticity centre was coupled with the poleward exit region of this upper jet, and that the period of maximum intensification occurred when the jet passed through the upper trough on the equatorward side of the surface disturbance.
The contribution of an upper level jet to cyclogenesis in the present case was examined using fields of geopotential height from RASP 500 hPa analyses (Fig. 7).
The 500 hPa analysis for 0800 WST 23 May 1994 (Fig. 7a) showed an 80 knot jet streak orientated almost north/south on the western side of a broad trough off the west coast, with the surface low being analysed under the right hand exit region. By 2000 WST (Fig. 7b) the area covered by the 80 knot jet isotach had expanded significantly and a 100 knot maximum was rounding the apex of the trough, with the surface low still in a favourable position for continuing development.
Another method of diagnosing the potential for surface cyclogenesis is to infer regions of thermal advection by examining the orientation of the surface isobaric pattern with the field of 1000-500 hPa thickness.
From an examination of the 0800 WST 23 May 1994 thickness and surface analysis (Fig. 8a) it appears that strong cold air advection is occurring in the southwesterly flow and that cold air advection is also evident in the west to northwest flow across the southwest of the state. This would imply that sinking motion and rising pressures would be occurring. However this reasoning is only true if we assume the low is stationary. If the north eastward translation component of 100 km/h is subtracted from the synoptic flow then in a storm relative sense strong warm air advection is occurring ahead of the system. By 2000 WST 23 May 1994 (Fig. 8b) similar reasoning would suggest that the storm relative warm air advection would be considerably stronger than that indicated.
5. COMPARISON OF NUMERICAL MODEL PERFORMANCE
Overall the forecast guidance provided by the numerical models was very good, with the US, EC and UK models shown in Figures 9a, 9b and 9c respectively. Cyclogenesis south of the state was predicted up to 72 hours ahead by all the models and the forecast latitude of the development gradually shifted northward towards the south coast approaching analysis time. At 24 hours prior to the event all models had produced a low below 990 hPa off the south coast. The UK and the EC models were very similar with the forecast position of the low south of Albany with central pressure 988 hPa (analysis pressure estimated to be 989 hPa). The US for the same time indicated a slightly deeper low, located further northwards.
In terms of the pressure gradients across the south west of the state all prognosis suggested the likelihood of gale to storm force winds about the south west coast on the 24 hour forecast. The observed pressure gradient form Geraldton to Albany at 2000 WST 23 May 1994 was 17 hPa compared with 15 hPa, 18 hPa, 22 hPa for the EC, UK, US prognosis respectively.
(Fig. 9d GASP model and Fig. 9e RASP model.)
6. COMPARISON WITH OTHER MAJOR STORMS.
Fremantle Port Authority wind data from the period 1963 to 1993 was examined in order to identify major wind storm events. Events were ranked on the basis of maximum gusts recorded, duration of wind speeds above 55 km/h and the average speed during that period and four of the strongest events since 1975 were chosen for comparison with the May 1994 storm. A summary of the impact of these four events on communities in the southwest follows:
(a) 4 April 1978 (TC Alby)
Tropical Cyclone Alby passed close to the southwest corner of WA on 4 April 1978 killing five people and causing widespread but mostly minor damage to the southwest. One man was blown from the roof of a shed and a woman was killed by a falling pine tree. Another man was killed when a tree fell on the bulldozer he was operating and two men drowned at Albany when their dinghy overturned. Fires fanned by the very strong winds burned an estimated 114 000 ha of forest and farming land. The damage bill was estimated to be $32 million (1991 dollars).
(b) 8 June 1981
Strong, squally winds, accompanied by heavy rain, produced widespread damage about the southwest coast. Perth metropolitan area was littered with fallen tress and power lines and the debris from damaged buildings. Damage extended north to Geraldton, inland to Northam and south to Harvey with the total cost of the event unknown.
(c) 28/29 June 1983
This storm was responsible for widespread damage in the southwest including the loss of two lives. A man was killed in a road accident directly attributed to bad weather and a crew member on a visiting American air craft carrier was killed when high winds crushed the man behind an open door. The storm downed trees and power poles with blackouts lasting up to three days after the event. Heavy rainfall associated with the storm caused river levels throughout the south west to rise rapidly, flooding paddocks and cutting roads. The damage bill for this storm was estimated to be greater than $1 million (1983 dollars).
(d) 22 September 1988
A severe storm battered the south of the state, causing extensive damage throughout the southwest from Perth to Albany. Hundreds of roofs were damaged and several ripped off entirely, trees were downed and power was lost to over 100 000 homes in the metropolitan area. Damage was sustained to about twenty boats in the Perth area after breaking their moorings. Severe damage was also done to Perth market gardens and vineyards. The cost of the September storm was estimated to be $8 million (1991 dollars).
7. COMPARISON OF SYNOPTIC DATA FOR MAJOR STORMS IN THE SOUTHWEST.
Table 1 provides a comparison of wind data from the FPA for each of the events. One of the most noticeable features of the May 1994 storm was the number of gusts greater than 129 km/h (25) being more than three times the number recorded for any other event. The peak 30 minute mean wind of 107 km/h was also the strongest, however the maximum gust of 147 km/h was recorded in the September 1988 event. The FPA anemograph traces for each event are given in Fig.10a, Fig.10b, Fig.10c, Fig10d.
DATE
PEAK WIND GUST (km/h) DATE/TIME*
No GUSTS >=129 km/h (70Kn)**
DURATION (h)WIND>55 km/h (30Kn)
MEAN WIND (km/h)***
DURATION (h)WIND> 93km/h (50Kn)
PEAK 30 MIN MEAN WIND (km/h)
23/24 May 1994
143
0220 24 May 1994
25
17
80
3
107
22 Sept. 1988
147
0130 22 Sept. 1988
8
16
69
3
100
28/29 June 1983
131
2230 29 June 1983
2
20
74
3
102
8 June 1981
143
2210 7 June 1981
8
36
70
5
98
22 July 1981
131
0900 22 July 1981
2
22
67
0
89
4 April 1978
143
1600 4 April 1978
6
7
85
4
102
6 April 1969
133
2300 6 April 1969
2
6
74
0
85
*All times are WST
**Number of gusts estimated from anemographs.
***Mean wind during the period when winds were greater than 55 km/h(30Kn).
Three hourly surface synoptic data was examined for each event to obtain pressure values at Bureau stations around the southwest and to calculate the pressure gradient across the region. This information is provided in Table 2. The mean sea level pressures at Albany were all between 985 hPa and 981 hPa while Perth pressures ranged from 991 hPa to 1002 hPa (but were mainly under 998 hPa). With the exception of the June 1983 event when the Geraldton to Albany pressure gradient was 17 hPa, the gradient in all other events was between 20 and 21 hPa. The change in the pressure gradient 12 hours prior to and 12 hours after the period of maximum gradient was also calculated to provide an indication of how rapidly the gradient was changing. While pressure gradients for the June 1981 and June 1983 storms were large (16 hPa for each) 12 hours prior to the maximum, the gradient for the other three events was relatively small, indicating a rapid increase had taken place.

The tidal elevations (Fig.3) for 23 May 1994 storm and for TC Alby were compared at the Fremantle Fishing Boat Harbour site (Fig.11). Although the storm surges associated with the 23 May 1994 storm and TC Alby were similar in peak heights, the surge was sustained for a longer period of time in the May 1994 storm.
DATE
TIME OF MAX PRESSURE DIFFERENCE
GERALDTON/ALBANY PRESSURE DIFFERENCE(hPa)
PRESSURE GRADIENT GERALDTON/ALBANY 12 HOURS BEFORE MAX(hPa)
PRESSURE GRADIENT GERALDTON/ALBANY 12 HOURS AFTER MAX(hPa)
PERTH MINIMUM PRESSURE(hPa)
ALBANY MINIMUM PRESSURE(hPa)
23 May 1994
2300
21.0
11.0
15.0
994.0
988.0
22 Sept. 1988
0200
21.1
7.0
6.5
997.9
986.5
28 June 1988
2300
17.0
16.0
12.8
996.0
987.9
22 July 1981
1100
14.4
12.7
12.9
993.6
986.8
8 June 1981
0500
20.4
16.0
7.1
1002.4
989.0
4 April 1978
2300
20.0
0.4
0.1
991.0
991.3
6 April 1969
0300
17.0
-4.0
7.0
1001.0
994
The sequence of synoptic charts accompanying the winter storms showed striking similarities. Fig. 11a and Fig 11b shows 0900 WST MSL pressure charts on successive days during each event. For all winter cases the storm was preceded by the passage of a primary front across the southwest of the state. This was then followed by vigorous secondary upstream development, due to cyclogenesis in a polar airstream.
In three cases (Fig.12 a,c,d) the low originated form the area between 100oE and 110oE in the latitudes south of 40oS before moving rapidly northeast towards the south west corner. From this point the low intensified rapidly as it moved into the Bight. In the fourth case the cyclogenesis occurred further to the west and the system moved on a more eastwards trajectory towards the south west corner. In all cases the cyclogenesis resulted in a low with central pressure near 984 hPa or less located just off the south coast moving in a south easterly direction.
The case of TC Alby was a classic tropical cyclone capture event in that the storm maintained a considerable intensity and accelerated rapidly south eastwards in advance of an amplifying mid latitude frontal system.
8. IMPLICATIONS FOR FORECASTING DURING SEVERE WINDSTORMS
As a result of the study of the May 1994 storm and the other winter events some implications for forecasting during these events can be drawn.
� Forecasters should be wary of the rapid increase in the pressure gradient and hence in wind speeds that can occur when rapid cyclogenesis takes place near the south coast. A combination of the existing pressure gradient combined with numerical model guidance should be used for predicting storm severity.
� Forecasters should try to infer storm relative thermal advection when a system is translating rapidly.
� If intense cyclogenesis is forecast near the south coast (with a corresponding increase in the Geraldton to Albany pressure gradient towards 20 hPa) then:
-a storm warning for shipping northwards to Jurien Bay should be considered with rough seas and high swells forecast.
-a severe wind warning for the general community should be issued indicating the potential for wide spread damage to property in the southwest with wind gusts up to 130-140 km/h.
-airport warnings and sigmets for low level turbulence should be considered.
-higher than normal tides causing flooding of areas near the ocean and river foreshore are possible.
9. SUMMARY
The storm of 23/24 May 1994 ranks alongside TC Alby as one of the two strongest to affect the southwest of the state since 1963. In the Perth metropolitan area both the maximum 30 minute mean wind and the number of wind gusts greater than 130 km/h was higher in the May 1994 storm, however in the southwest corner of the state (southwest of a line Mandurah to Albany) the winds associated with TC Alby were stronger.
The low that caused the damage originated from the high latitudes to the southwest of the state and moved northeastwards at an average speed of 100 km/h. It passed just to the south of Perth around 2000 WST 23 May 1994 and then deepened rapidly while moving south eastwards into the Bight and merging with another low further to the south. The intensification of the low was seen to be a result of the movement of the polar front jet around the apex of a thermal trough near the west coast in a similar fashion to that described by Sinclair and Cong ,1992. The thermal advection fields, as inferred from inspection of the 1000-500 hPa thickness analyses and the surface isobaric pattern, were misleading in this case due to the rapid translation speed of the low. In a case such as this storm relative flow should be used when determining the thermal advection pattern. Numerical model predictions of the cyclogenesis provided generally good guidance out to 72 hours ahead.
A comparison of the synoptic weather charts that accompanied the May 1994 storm showed many similarities with 3 other major winter storm events that have occurred in the past 20 years. In all these case the lows developed due to cyclogenesis in the cold air field to the rear of a leading frontal band. The lows intensified as they moved eastwards near the south coast deepening to below 985 hPa during their passage into the Bight. The lows generated very strong pressure gradients across the southwest as measured by the Geraldton to Albany pressure difference, which generally increased to around 20 hPa at the peak of the storms.
References
Commonwealth of Australia: Results of Rainfall Observations made in Western Australia 1929, 387pp
Guymer, L.B., 1978 : Operational application of satellite imagery to synoptic analysis in the southern hemisphere. Tech. Rep. 29, Bureau of Meteorology, Melbourne, Aust.
Sinclair, M.R., and X. Cong, 1992 : Polar airstream cyclogenesis in the Australasian region: A composite study using ECMWF analyses. Mon. Wea. Rev., 120, 1950-1972.




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Re: 20 years ago today - May 1994 storm

Postby Fu Manchu » Fri May 23, 2014 11:50 pm

JR shared the synoptic for the 24th as well.
Image


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Re: 20 years ago today - May 1994 storm

Postby brayden » Fri May 23, 2014 11:50 pm

There was a report/case study written up for the event though its on the internal BOM server.

1. INTRODUCTION

On the evening of 23 May 1994, through until the early hours of the following morning, a severe windstorm battered the southwest of Western Australia causing widespread damage, particularly in coastal communities between Mandurah and Geraldton. The strongest sustained winds occurred for a period of about an hour around 2000 WST , but violent squalls in showers continued on throughout the night. The impact of the storm was made more considerable in that it followed a long period of dry stable conditions over much of the southwest of the state.

The windstorm was the most destructive weather event to affect the Perth Metropolitan area in the last 30 years, the total damage bill was greater than 25 million dollars. Several houses were completely unroofed but the majority of property damage was minor, the average insurance claim being $700 and more than 60% of claims were for fence damage. Thousands of trees were either blown down or had large limbs snapped off. Many of these fell across powerlines contributing to widespread blackouts. The number of households affected was so large that power was not fully restored for several days. Examples of the damage caused by the storm can be seen in Fig.1.

Two people on board a yacht sailing from Fremantle to the Cocos Islands were caught in the storm off the coast from Jurien Bay and were lost at sea, presumed drowned. Huge seas and above normal tides caused significant erosion to beaches and parts of the Perth river foreshore were also inundated. Fortunately there were no serious injuries or loss of life on land.

Severe winter gales have been part of the weather history of the region. Periodic accounts of winter storms, from the time of settlement in 1830 through until 1928.

2. DATA

Wind

Power failures affected the availability of data during the event at a number of centres. The highest wind gust recorded during the storm was 143 km/h at Swanbourne automatic weather station (AWS) and much the same at the Fremantle Port Authority tower (height 60 m) assuming a 15 km/h correction due to a faulty pen setting. Other metropolitan recordings included Rottnest Island 133 km/h, Jandakot airport 130 km/h and Perth airport 111 km/h. To the north Geraldton recorded a gust to 128 km/h, the strongest gust for May on record, while in the lower southwest wind gusts recorded were considerably lower. Mandurah recorded 119 km/h, Bunbury Power Station 95 km/h and Albany 93 km/h. Further to the east Jacup AWS registered a gust to 107 km/h and Esperance 130 km/h.
Pressure

The approach of the low was signalled by strong surface pressure falls across the southwest. At Perth the barometer fell 10 hPa in the nine hour period from 0900 WST to 1800 WST on 23 May, when a low of 994.3 hPa was recorded. The lowest pressure recorded over the mainland during the storm was 986.6 hPa at Jacup AWS at 0001 WST 24 May. At Albany the barometer fell to 989.3 hPa at 0001 WST 24 May and at Esperance to 987.7 hPa at 0120 WST 24 May.

Rainfall

Although widespread rain accompanied the passage of the front and low across the southwest rainfall totals were not unusually high. This was attributed to the rapid movement of the system. The isohyetal analysis for the twenty four hours ending 0900 WST 24 May 1994 (Fig. 2) showed a maxima greater than 40 mm over the ranges to the east and southeast of Perth and between Cape Leeuwin and Albany.

Storm Surge

One of the consequences of strong winter storms in Perth, including the 23 May storm, has been the inundation of the river foreshore near the city centre due to higher tides. The tidal elevation measured at the Fremantle Fishing Boat Harbour compared to the predicted tide level (Fig. 3) showed a storm surge of 0.98 occurred at 2034 WST 23 May. The potential for more serious and extensive flooding was not realised in this case as the peak surge occurred near the time of predicted low tide.

Seas and Swell

Two ships located near 30oS 114oE (just off the coast near Jurien Bay) provided information about wind speeds, sea state and swell during the period of the event. At 1400 WST 23 May 1994 seas between 2.5m and 4m and swell between 3m and 4m were being reported. By 0300 WST 24 May 1994 seas had risen to 5-5.5m and the swell had increased to 8-9m. The seas and swell began to ease after 0800 WST 24 May 1994 and were being reported at 2m and 5.5m respectively by 1500 WST 24 May 1994.


SUMMARY

The storm of 23/24 May 1994 ranks alongside TC Alby as one of the two strongest to affect the southwest of the state since 1963. In the Perth metropolitan area both the maximum 30 minute mean wind and the number of wind gusts greater than 130 km/h was higher in the May 1994 storm, however in the southwest corner of the state (southwest of a line Mandurah to Albany) the winds associated with TC Alby were stronger.

The low that caused the damage originated from the high latitudes to the southwest of the state and moved northeastwards at an average speed of 100 km/h. It passed just to the south of Perth around 2000 WST 23 May 1994 and then deepened rapidly while moving south eastwards into the Bight and merging with another low further to the south. The intensification of the low was seen to be a result of the movement of the polar front jet around the apex of a thermal trough near the west coast in a similar fashion to that described by Sinclair and Cong ,1992. The thermal advection fields, as inferred from inspection of the 1000-500 hPa thickness analyses and the surface isobaric pattern, were misleading in this case due to the rapid translation speed of the low. In a case such as this storm relative flow should be used when determining the thermal advection pattern. Numerical model predictions of the cyclogenesis provided generally good guidance out to 72 hours ahead.

A comparison of the synoptic weather charts that accompanied the May 1994 storm showed many similarities with 3 other major winter storm events that have occurred in the past 20 years. In all these case the lows developed due to cyclogenesis in the cold air field to the rear of a leading frontal band. The lows intensified as they moved eastwards near the south coast deepening to below 985 hPa during their passage into the Bight. The lows generated very strong pressure gradients across the southwest as measured by the Geraldton to Albany pressure difference, which generally increased to around 20 hPa at the peak of the storms.

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Re: 20 years ago today - May 1994 storm

Postby brayden » Fri May 23, 2014 11:51 pm

Ah I see he gave ya the details lol sorry
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Re: 20 years ago today - May 1994 storm

Postby Fu Manchu » Fri May 23, 2014 11:54 pm

IR sat image.
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Another BoM report on the event:
http://pandora.nla.gov.au/pan/55863/200 ... html#local


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Re: 20 years ago today - May 1994 storm

Postby Fu Manchu » Fri May 23, 2014 11:57 pm

Huge thanks goes to John Relf for the help digging up the info.


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Re: 20 years ago today - May 1994 storm

Postby Fu Manchu » Fri May 23, 2014 11:58 pm

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Re: 20 years ago today - May 1994 storm

Postby Fu Manchu » Sun May 25, 2014 6:30 am

Good to note also the pressure gradient Albany to Gero.
Something to use as a guide for how nasty a system maybe. JR explained it to me once. Quite sure 25 was ugly ugly and 19-20 was just ugly. (Not his words :) )

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Re: 20 years ago today - May 1994 storm

Postby floppy » Sun May 25, 2014 6:54 am

wasn't there but all this reminds me of August 2000
in fact there were two a few weeks apart but it was August's that I remember
because I was in the SES ( Albany ) at the time and Albany copped a real beating

Fu Manchu wrote:Records from the Fremantle Port Authority(FPA) since 1963 show that severe winter storms have affected the southwest on average about once every five years. Despite these being relatively infrequent, their impact on the southwest region can be considerable and to date no meteorological studies of these events have been published.


yeah I seem to remember another severe event about 5-6 yrs after that too
2005 was when Bunbury Cathedral copped it
we must be due another this year
you can never always sometimes tell
when you least expect the most

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Re: 20 years ago today - May 1994 storm

Postby Blue Skies » Sun May 25, 2014 11:53 am

Just to pick a point out of that extensive report to clarify - there was a polar jet stream on the back side of the low giving it extra spin, and this allowed the winds to get faster than normal?
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Re: 20 years ago today - May 1994 storm

Postby Benni.G. » Thu May 29, 2014 11:58 am

I remember this storm like it were yesterday, I was in Roleystone back then. The winds were stronger then any cyclone I have been in up here, the strongest being a cat 2.
We had a large jarrah tree topple over onto another tree, which then toppled over and was hanging above the house. The Jarrah tree now resembles a very nice dining table
There was a mass city - wide blackout 2 months prior to this, caused by pole top fires.
On the topic of nasty winter storms, I remember driving to work early one morning to come across a garden shed standing in the middle of the road, nothing like playing dodge first thing after you wake up lol
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