Category Archives: natural disasters

Disasters that are attributed to natural causes

North Indian Ocean – Tropical Cyclone Tauktae – 15 to 18 May 2021

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A look at the Worlds tropical cyclone tracks will reveal that the majority of all tropical storms form within certain ocean areas including the north west Pacific Ocean, an area of the west coast of Central America and Mexico, the tropical Atlantic Ocean north of the Equator including the Gulf of Mexico, the Western Pacific Ocean including areas within Australian waters and the tropical Indian Ocean within the southern hemisphere between Australia and Africa.

There is also another area where such storms can occur but are much less likely being the North Indian Ocean situated between India and the Arabian Peninsula. Occasionally a storm will form within this area and track towards the North West India / Southern coast of Pakistan but instances of such occurrence are relatively rare.

During the period 15 to the 18 May 2021 a significant tropical storm has formed within an area where tropical cyclones are generally rare. This storm was named Tropical Cyclone Tauktae which formed off the west coast of India then tracked northwards towards the north west coast of India and even threatened the south east coast of Pakistan. Landfall occurred between Porbandar and Mahuva (Gujarat State - India).

At peak intensity, this storm reached Category 4 on the Saffir Simpson Scale with peak wind gusts at the core of at least 115 knots (Approximately 213 km/h). This storm was supported by ocean waters within the range of 30 to 31C and atmospheric conditions were certainly favourable for supporting such a strong storm. Strong convection and thunderstorm cells were visible on satellite images especially to the south of the eye which supported the storm. This storm weakened just before commencing landfall over Gujarat State.

This storm has brought heavy rain especially around Saurashtra and numerous west coast localities were warned for heavy rain as the storm tracked northwards. Media reports suggests a significant impact onto the north west Indian coast with at least 26 fatalities mainly within coastal locations, flooding, heavy rain and intense wind gusts. It is believed that upwards of 200,000 residents were evacuated prior to the storm making landfall.

The images attached to this post are taken from Worldview and CIMSS. Information was also sought from the India Meteorological Department 17/5/2021 prior to the storm making landfall.

Tropical Cyclone Seroja at landfall – How strong was the storm? 12/4/2021

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Tropical Cyclone Seroja has made landfall very close to the town of Kalbarri in Western Australia and has caused some significant damage to the town. In addition, the regional city of Geraldton was also impacted by gale force and damaging winds including a period of heavy rain as the storm passed over.

The storm was travelling unusually fast at landfall and reached a speed of at least 55 km/h. It had a relatively narrow track as it traversed over land towards the south east.  

Media reports have indicated that peak wind gusts reached 170 km/h and that the storm was a Category 3 system upon landfall.

While verified data is still being processed and updated, a number of weather stations within proximity of the storm have recorded the following peak wind gusts:-

Geraldton Airport - 120 km/h at 8.52 pm and 8.57 pm. However, not recorded in the detailed notes, a single peak gust of 121 km/h was recorded at 9 pm according to data taken from “Australian Weather News”.

Furthermore, significant peak wind gusts at Geraldton Airport occurred mainly between 8.23 pm and 9.08 pm on Sunday evening.

Morawa Airport - A single peak wind gust of 119 km/h occurred at 11.26 pm.

Shark Bay - Maximum peak wind gusts of 91 km/h occurred.

According to observations taken from the following sites (Taken from “The Australian Weather News” 12/4/2021)

Binnu Agricultural Station - A peak wind gust of 122 km/h occurred at 8.04 pm.

Morawa Agricultural Station - A peak wind gust of 132 km/h occurred at 11.21 pm.

At the present time, additional verified data is not available and the above represents the highest identified wind gusts known as at 8 pm 12/4/2021 (Sydney Time - New South Wales).

Tropical Cyclones across the world are categorized according to their location. For example, across the Atlantic Ocean, Eastern and Central Pacific, the Saffir Simpson Scale is used and CIMSS models use the scale. Generally the National Weather Service (USA) uses the scale to determine the strength of a tropical storm.

Tropical Cyclone Seroja was determined to peak as a Category 1 system at landfall on the CIMSS models. A Category 1 storm has sustained peak wind gusts of between 119 km/h and 153 km/h and based on available data, this storm would fit the Category 1 storm system. If verified peak gusts of 170 km/h did occur, then it is possible that the storm reached Category 2 on the Saffir Simpson Scale.

Note - A Category 2 storm has maximum sustained peak wind gusts of between 154 km/h and 177 km/h on the Saffir Simpson Scale.

The Bureau of Meteorology uses a different scale for measuring the strength of tropical cyclones which makes a comparison somewhat confusing. The scale is called the “Australian Tropical Cyclone Intensity Scale” which was introduced in 1989/1990 and under this scale:-

A Category 1 storm has sustained winds of 63 to 88 km/h and with peak wind gusts of 91 to 125 km/h.

A Category 2 storm has sustained winds of 89-117 km/h with peak wind gusts of between 126 km/h and 166 km/h.

A Category 3 storm has sustained winds of 118-157 km/h with peak wind gusts of between 167 km/h and 225 km/h.

A Category 4 storm has sustained winds of 158-198 km/h with peak wind gusts of between 226 km/h and 280 km/h.

A Category 5 storm has sustained winds exceeding 198 km/h with peak wind gusts greater than 280 km/h.

Hence on the Saffir Simpson Scale, this storm appears to have rated Category 1, possibly Category 2 but under the “Australian Tropical Cyclone Intensity Scale”, the storm would have fit as a Category 3 system.

The Australian system for determining the strength of a tropical cyclone has lower thresholds than that of the Saffir Simpson Scale.

Hence, depending on what scale is used, the strength of Tropical Cyclone Seroja will vary and can be confusing.

The storm has all but decayed and for the 24 hours till 9 am 12/4/2021, a narrow band of rain of between 50 mm and 74 mm occurred along its path. The highest verified rainfall along its path for the is 24 hours is 76 mm at Binnu West.

Source

1 - Australian Weather News 12/4/2021.

2 - Bureau of Meteorology 12/4/2021 - Australian Tropical Cyclone Intensity Scale 1989/1990.

3 - National Weather Service - Saffir Simpson Hurricane Scale.

Addendum to topic - Peak wind gusts

Further to the above topic, further data has been identified in which a peak wind gust of 139 km/h occurred at Binnu West at 9.47 pm Sunday and the Bureau of Meteorology has identified a peak wind gust to 170 km/h at Meanarra Tower near Kalbarri at 7.03 pm on Sunday. They appear to be the higher wind gusts not appearing in the day to day data sets from surrounding weather stations.

Hawkesbury River Flood – The aftermath – 26 March 2021

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Floodwaters are now receding and the extent of the damage is becoming obvious. My wife and I returned to Windsor Friday afternoon 26 March 2021 to view the water levels. Floodwaters at that time were still high but receding and the new Windsor Bridge was clearly visible again.

Much rubbish, litter, tree branches and furniture items had washed downstream and unlike last Sunday, the floodwaters now had a distinct brown muddy colour and an odour.

Roads were still closed including the Windsor Bridge with assessors viewing the bridge for damage and with cleaning crews undertaking a mammoth cleaning task.

Floodwaters rose at least 2 metres in height along the Windsor Riverwalk and much scouring of soil had occurred. A distinct brown mark had been left on trees to show how high the waters came.

The cleanup will take some time and insurance costs will take time to tally. Preliminary estimates would suggest that this event will exceed $1 billion but it is too early to verify this. This event has been declared a catastrophe.

The extent of the flooding on Thursday can clearly be seen on this NASA Worldview image at a scale of 10 km from Earth orbit. The flood is seen as a muddy brown river with the floodwaters across North West Sydney clearly visible.

The photos attached show some of the cleanup that is needed at Windsor Bridge and other locales and there is a need to remove debris and even entire trees that had toppled over.

The rain event that caused this was prolonged across 5 or 6 days which is unusual and many coastal localities received more than 300 mm of rain with some areas receiving more than 400 mm of rain.

There are exceptions to this including Mt Seaview which received 815 mm of rain in 5 days during this event, Kempsey has received 819 mm of rain in 19 days this month including 758 mm of rain during the event.

All photos attached to this event were taken Friday afternoon 26 March 2021 around Windsor.

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