Category Archives: Tropical Cyclones

A large circulation sproducing heavy rainfall, very strong winds and storm surges

Tropical Cyclone Amos hits Western Samoa April 23 2016

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Tropical Cyclone Amos has taken a slightly altered path when compared to the forecast model suggested by CIMSS dated 22/4/2016.

As a result, the core of the tropical cyclone is either likely to brush the north coast of the Western Samoa or pass right over one or both the islands.

The satellite photo from CIMSS shows the storm directly over Western Samoa as a category 2 storm on the Saffir Simpson Scale with winds reaching 90 knots (Approximately 167 km/h) with higher gusts to 110 knots (Approximately 204 km/h). Heavy rain is a feature and forecasters are predicting as much as 500 mm of rain over certain areas. Given the mountainous terrain of the islands, rainfall is likely to vary in places and rainfall may be enhanced on the windward side of the mountains while the leeward side has less rainfall.

Flooding, storm surge and some property damage is certain.

The storm as forecast appears to be reaching maximum strength at the point the storm makes its influence felt across the islands.

Using NASA's Worldview,Satellite image, the population centres of Western Samoa (Shown in red) have been overlaid across the image. Given that the storm appears likely to now pass / brush across the north coast, the capital Apia would be significantly impacted by the event.

Another island being American Samoa is also likely to be significantly affected by the storm.

The satellite image does not show a defined eye but strong convection showing storms is identified.

The image from NOAA (CIRA) shows the storm directly over Western Samoa suggesting either a direct hit or very close to one.

Once the storm moves away from the islands, it is expected to weaken as it tracks south east over colder waters.

CREDITS

1 - CIMSS (Images of AMOS) dated 23/4/2016.
2 - CIRA (NOAA) Image dated 23/4/2016.
3 - NASA (Worldview) Population overlays provided dated 23/4/2016.

Tropical Cyclone Amos – A threat to Western Samoa April 22 to April 25 2016

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A new storm is gathering strength just to the west north west of the small South Pacific Islands of Western Samoa. This storm has been named “Amos”.

Considering its location and forecast track, it appears that this storm could threaten or significantly impact the islands in coming days. If the forecast models are correct and the storm maintains its forecast track then the western and southern side of Western Samoa could be impacted significantly by the storm. This would include towns such as Samataitai, Taga on Savai and Falelatai on Upolu.

On the island of Savai, Mt Mauga Silisili at 1,858 metres in elevation would serve to enhance rainfall while providing for rain shadows in other areas depending on the location of the storm.

The capital of Apia is located to the northern side of Upolu Island and may be spared the worst of any such storm due to a small mountain barrier lying to the south of the city.

The storm has just completed its transition to a Category 1 tropical cyclone on the Saffir Simpson Scale west north west of Western Samoa. The forecast model from CIMSS is suggesting peak strength being a Category 3 storm at the point where the storm makes its closest approach to Western Samoa.

A tropical cyclone must sustain winds of 65 knots (120 km/h) to be classed a category 1 storm. Forecast winds at the core may reach 105 knots or 194 km/h (Category 3) at the closest point the storm makes to both islands making it a dangerous storm and a storm that deserves attention.

Strong convection is occurring as the storm develops further. The environment is favourable and its position over seas of 30C to 31C in temperatures makes the location highly favourable to sustain such a storm. Its location so close to Western Samoa makes it a potentially dangerous storm for the islands.

Following its passage across the Western Samoa region, this storm is expected to track south east taking it over cold oceans where it will decay.

Note:- Due to the current location of the tropical cyclone, a direct satellite image of the storm is not available as it appears the location of the storm at 12.4 degrees south and 182.6 degrees east does not lie within the direct viewing range of NASA's TERRA or AQUA satellite networks.

CREDITS

1 - CIMSS (Forecast plot) for Tropical Cyclone Amos dated 22/4/2016.
2 - CIRA (NOAA) Satellites and information - Image acquired 22/4/2016.

Tropical Cyclone Fantala reaches Category 5 – April 18 2016

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Tropical Cyclone Fantala has become the most powerful storm this season across the southern Indian Ocean (South of the equator). This storm is now a serious threat to the northern coast of Madagascar with the southern outermost bands of rain and storms passing over the northern coast of the country.

The worst of the storm is out to sea and forecast models suggest the storm to stall then head back south east. This storm has already defied earlier models as it has:-

1 - Reached category 5 on the Saffir Simpson Scale.
2 - Has tracked much closer to Madagascar then initially expected.

As shown on the graph from CIMSS, there is evidence that the storm is sustaining winds of 150 knots at the core (Approximately 278 km/h) and it is possible that wind gusts are reaching as high as 175 knots or 180 knots (Approximately 324 to 333 km/h). This makes it a formidable storm and any landfall on Madagascar or populated nearby islands at this strength would be disastrous.

It appears that the storm is at peak strength and should commence a slow weakening but it will remain a significant threat to the northern and north eastern coasts of Madagascar for a few days.

The NASA satellite photo of the storm taken 17/4/2016 from MODIS Terra shows a thick circular cloud mass, deep convection and a well defined eye at the centre. The CIMSS infra red image equally shows an intense storm barely off the coast of Madagascar and direct north of Antsiranana.

An image of the storm from CIRA (Enhanced Infrared MODIS /AVH RR) clearly suggests a powerful and formidable storm (Date 18/4/2016).

It will be interesting to see what occurs given its proximity to landmasses and population centres over coming days.

CREDITS

1 - CIMSS (Forecast plot of the storm dated 18/4/2016).
2 - NASA (Worldview image) 17/4/2016.
3 - CIRA / NASA (MODIS) AVH RR 18/4/2016.

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