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Weather Warning for the Weekend (2-4 March 2012)

The Weather service has issued a weather warning regarding Tropical Storm IRINA - expected to become a proper cyclone by the end of the weekend.

Attached is a press statement dated yesterday but it has some really good info for travelers.  Expected impact areas in SA are KZN, Limpopo and parts of Mpumalanga – the eastern areas.  Predicted rainfall could exceed 400mm per 24hr period.

Call centre -  just as a heads up to the contractors in those areas.

Press Statement

DATE: 01 MARCH 2012
FOR IMMEDIATE RELEASE
TROPICAL STORM IRINA ON THE WAY TO SOUTHERN MOZAMBIQUE AND PARTS OF SOUTH AFRICA DURING THIS WEEKEND

Current Situation

At 1400SAST this afternoon, Moderate Tropical Storm "IRINA" was located at 19.5 S / 043.7 E within the central part of the Mozambique Channel, just on the west coast of Madagascar, near the town of Maintirano. The eye of the system is somewhat obscured at the moment, but the distinctive spiral banding features, characteristic of such systems, are nevertheless well-defined. "IRINA" is currently moving southwards at 13 knots (24 km/h).

Earlier in its lifetime, the storm had its origins over the open ocean, eastwards of Madagascar. It moved mainly westwards, directly over the landmass of Madagascar, weakening the system significantly. However, a number of environmental factors in the Mozambique Channel remain favourable for sustainable development of tropical cyclones and consequently the system has re-organised and progressively deepened (intensified) over the last few days.

Values of sea-surface temperature (SST) remain significantly elevated over the ocean region of the west coast of Madagascar, with observed values of SST of the order of 29˚C to 31˚C, thus providing the main source of energy, driving such tropical systems. Furthermore, the airflow in the uppermost regions of the storm is such that rising air (from the core of the storm) is rapidly carried away at high altitude. Such airflow is ‘divergent’ in nature and is a key feature of sustained development of the storm. Whilst there are numerous such "ingredients" that contribute positively towards tropical cyclone development, it is notable that there are currently no negative factors that could lead to the short-term weakening or decay of the system. On the contrary, it seems likely that within the following 48 hours, the system is anticipated to intensify to attain full "Tropical Cyclone" status.

Expected Sequence of Events

Whilst the current track of "IRINA" is a predominantly southward one, it is predicted that the track will shift towards south-west at the beginning of the weekend. The ensemble output from ECMWF (Figure 2, below) is suggesting with a fairly high degree of sustained confidence, that once the south-westward movement is adopted, it will most likely result in the system maintaining this track, resulting in landfall close to Inhambane and Xai-Xai in the early morning hours of Monday 5th March (and ultimately the general area around Maputo later on Monday).

Furthermore, once the system is in the general area of Maputo, Mozambique, it seems most probable at this stage that the system will slow down and ‘stall’ for a period of about 48 hours. The reason for this is that an upper-air ridge over southern Africa is expected to form a buffer or obstacle, preventing the southward escape of the tropical system.

Impacts on Southern Africa

As can be seen from the sequence of predicted rainfall (figures 3 to 5 below), it is highly likely that an episode of widespread heavy to torrential rain can be expected over a large portion of southern Mozambique as well as eastern Limpopo province, eastern Mpumalanga, KwaZulu-Natal (especially in the north at first) as well as Swaziland.

Within the regions mentioned above, areas PARTICULARLY AT RISK would be the southern coast and adjacent interior of Mozambique, between Inhambane and Ponte do Ouro, extending down to include the Maputaland coast and adjacent interior of extreme north-eastern KwaZulu-Natal. Kosi Bay, St Lucia as well as Richards Bay are thus also considered to be well within the high risk region. These areas can expect accumulated rainfall of the order of 300 to 400mm over 2 to 3 days. This is rainfall of an extreme and exceptional nature (last experienced in this region when tropical cyclone DOMOINA affected KwaZulu-Natal in 1984, when 400 to 600mm was recorded over a similar period). Marine storm surge (a local sea rise of sea level in close proximity to the core of the tropical storm) as well as gale-force winds are also likely along aforementioned coastline.

To a somewhat lesser extent, the adjacent regions of eastern Limpopo province, eastern Mpumalanga, the remainder of KwaZulu-Natal and Swaziland could easily experience 100 to 200mm of accumulated rain during the period Sunday to Tuesday. Water flow entering river systems and dams within this sub-region is quite likely to exceed the carrying capacity of the rivers across a widespread area. The danger of flash-flooding and localised washaways should also be kept in mind. The public are therefore urged to be extremely cautious and (if possible) to avoid crossing swollen rivers, either on foot or by vehicle.

An additional topographic feature of Mpumalanga and Limpopo is the Eastern Escarpment region, which (through orographic lifting of moisture-laden air) is likely to significantly enhance rainfall on the windward (eastern) side of the Escarpment. Rainfall along this geographic area is likely to be of the order of "more than 200mm" at places over a two to three day period.

Finally, with the escape of IRINA being blocked by an upper-air ridge (as alluded to above), the last weather-related mechanism we need to consider is the expected arrival of a surface ridging high, around the southern tip of the continent, introducing fresh southerly to south-easterly airflow along the eastern seaboard (including KwaZulu-Natal) of South Africa, between Monday and Tuesday (as per figures 4 and 5 below). This is likely to sustain and enhance the heavy rain conditions along the KwaZulu-Natal coastline and interior, thus exacerbating the effects of an already severe weather pattern.

The South African Weather Service further wishes to state that the public can rest assured that the situation will continue to be closely monitored 24/7 throughout the weekend and beyond.

Further updates regarding this weather system will be issued at regular intervals to keep the public informed.

What common-sense precautions should I take?

  • Avoid crossing strongly-flowing / flooded rivers at causeways or drifts (this advice is equally valid for pedestrians as well as motorists).
  • Dwellings very close to rivers or within floodplains should be evacuated timeously (Farmers would be best advised to move river water pumps to higher ground).
  • Small to medium sized boats and fishing craft (operating along the coastline mentioned above) should return to port timeously.
  • Small fishing boats should be moved well above the normal high-water mark and firmly secured, as storm surge can be expected to raise local sea-levels by as much as 15 to 18 feet (3 to 6 m), particularly on the southern (poleward) side of the tropical storm.

Issued by: South African Weather Service (SAWS)

For media enquiries contact:
Ms Hannelee Doubell (Manager: External Communications)
Tel: (012) 367 6104 Cell: 072 222 6305
E-mail: hannelee.doubell@weathersa.co.za  

For technical enquiries contact:
National Forecasting Center
Tel: 082 233 9800
E-mail: nfc@weathersa.co.za  

Source: http://www.weathersa.co.za/web/

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