DIRECTION INTERREGIONALE ANTILLES-GUYANE

Transcription

1 DIRECTION INTERREGIONALE ANTILLES-GUYANE SUMMARY OF THE 2010 HURRICANE SEASON IN THE FRENCH WEST INDIES ( Martinique, Guadeloupe, St Barthelemy and St Martin ) Among the nineteen named tropical cyclones of the 2010 hurricane season, two directly hit the French West Indies (Earl in St-Martin/St-Barth and Guadeloupe; Tomas in Martinique) and a third one, Fiona, following Earl very closely, was a threat for the northern islands, leading to warnings from the authorities. No deaths were reported during the two severe events but St-Martin/St-Barth experienced damage, locally heavy, from Earl; in Martinique,the agriculture sector suffered from Tomas. It has to be noted that the FWI also experienced damage from flash floods associated with non (or pre ) tropical cyclone features, or from frontal systems on Christmas eve for example. These severe weather events are detailed below, with meteorological and hydrological data, consequences and warnings that were issued. Tropical Storm ANA :

2 Hurricane EARL Hurricane EARL was quite a typical cap verdian hurricane, with a classic track. The predictability was high and led to a good lead time. The first bulletin with yellow level for a cyclone threat was issued at noon on the 27 th, around 60 hours before the hit. St-Barth / St-Martin : The east part of the eye wall was the most active part and gave around 100mm of rain and gusts up to 150 km/h, maybe more in exposed areas, (see fig earl-1 below) in the morning of the 30th. It has to be noted that both St-Bath and St-Martin stations are relatively protected from South-Westerly winds which appeared to be the most violent due to the structure of Earl. Mean waves were estimated (from human observation, extrapolation and correlation with waveriders in Guadeloupe, buoys around and numerical models) around 6 meters with peak waves up to 8 to 9 meters. Gustavia harbour (St-Barth) and the port infrastructure were completely flooded and numerous boats were sunk. In St-Martin, some rooves were blown away and the infrasture exposed to high waves experienced some damage (Baie Nettlé). Power failures and issues with water supplies were also part of the consequences of the passage of Earl. Guadeloupe : Guadeloupe also experienced heavy rain and thunderstorms with gusts over 100km/h, in the spiral bands more than 200 km from the center of the hurricane. Rain accumulations were around mm with peaks locally up to 170mm but intensity was very high (100mm at the Airport from 15 to 18h on the 29 th afternoon). As a consequence, numerous floods were observed and lot of power failures brought some difficulties to the public. Guadeloupe also suffered from damaging waves which were measured north of Grande-terre with mean wave height around 5m and peak above 7m (see fig earl-2 below).

3 Fig Earl-1 : wind-gram (St-Barth and St-Martin) during the passage of Earl 2010 Fig Earl-2 : data from the waverider in Guadeloupe during the passage of Earl 2010

4 Tropical Storm FIONA Tropical Storm Fiona did not hit the FWI directly but it was a threat, just after the passage of hurricane Earl with a forecast track that was fairly similar. As the vulnerability of the northern islands was higher due to the consequences of Earl and since the forecast track uncertainties cone was very close to the islands (see fig Fiona 1), they were placed under vigilance, especially during the 1 st September. No specific data was recorded concerning rainfall, wind or waves. Fig Fiona-1 : Sat. Vis 1km, 31/08 at 11Z + forecast from 31/08 at 09Z

5 Hurricane TOMAS Tomas was a surprising late season barbadian type hurricane that developed very rapidly close to the southern Lesser Antilles. There was a large consensus from the NWP for a slow intensification with a track staying relatively south. On the 29 th, the system was not named yet but Meteofrance decided to anticipate (it was Friday ) an intensification of the system that could lead to tropical storm conditions over Martinique and to start issuing watches and a warning at midday. Fig Tomas-1 : Sat. Vis 1km+ forecast; 29/10 at 21Z

6 During its passage in the St-Vincent channel, Tomas brought tropical storm conditions over Martinique with quite a long duration of 1 sustained winds above 34 kt (almost 24 hours) on 30 th October (see fig Tomas-2 below). At the low level sites, wind were measured aroud 35 kt (10 average) with gusts above 50 kt but it has to be noted that the vertical distribution had a strong gradient and the wind at 500m was much stronger (Morne des Cadets AWS probably amplified by summit and ventury effects: Max 1 sustained wind 70 kt; max gust 93 kt gusts above 70 kt during 20 hours!) Fig Tomas-2 : 10 mean wind and gusts at Lamentin Airport and Vauclin As for the rainfall, 24 hours accumulation was measured between 150 and 200mm in numerous sites in Martinique, with a peak (220mm) in the extreme south range (see fig Tomas-3) Fig Tomas-3

7 The passage of hurricane Tomas in the south of the Lesser Antilles was well captured by the radar of Martinique. Fig Tomas-4 Verification of the rainfall accumulation with AWS and raingauges has shown that the information in term of Z/R law and rainfall aaccumulation from the radar and the panthere system (MétéoFrance software) was reliable. From the 24 hours accumulation information (see Fig Tomas-5 ), from 30/10 12Z to 31/10 12Z, we can estimate that the range in south Martinique experienced between mm of rain, while a large part of St- Lucia has been affected by at least mm, considering that these values could be underestimated a bit due to earth s rotundity. Fig Tomas-5

8 The cyclonic swell (swell + wind waves) was also well measured by the waveriders network. In the Saint-Lucia Channel, significant waves (H 1/3) above 4 meters were recorded during 7 to 8 hours (peak H 1/3 : 5meters) and maximum waves above 5 meters during 12 hours on the 30 th (peak max wave : 7.3 meters). (See Fig Tomas-6) The range of periods was very wide, mixing short periods (wind waves below 8 seconds) and long periods (swell, above 12 seconds) Obviously, the waves were decreasing further north and only the south shore of Martinique was impacted, but only lightly because the direction remained East (see Fig Tomas-7) Fig Tomas-6 Fig Tomas-7 Consequences : The peak of the tropical storm conditions were during the day; however, neither death nor injuries were reported. The agriculture suffered a lot, and especially banana plantatiosn that were partially destroyed (around 60%, to be confirmed). The fishing community, especially in the south of Martinique was also impacted (numerous loss of tools). Around people were affected by power failures during almost 2 days

9 Other notable severe weather events Several events of heavy rain associated with flash flooding also impacted the FWI last year, not only during the rainy season. It is also important to rememeber that not only tropical cyclones can give severe weather. Most of the time, for this kind of rapidly developing severe event, the predictability is very poor and the lead time is very difficult if the authorities do not want to risk a false alarm. - As examples, 2 events in Martinique and 1 in Guadeloupe; the important return period of these events led to the recognition of natural disasters for the impacted communities June 2010: in the rear branch of a disorganised tropical wave, the orographic effect strongly enhanced convection over the basse-terre of Guadeloupe; Almost 200mm in 2 hours and above 300mm in 6 hours were recorded by automated rain gauges - 04 October 2010: Again, in the rear branch of a tropical wave, a squall line developed in a south-westerly warm, humid and convergent flow. Due to orography blocking and effect, a small part of the central caribbean coast of Martinique experienced violent rain, with 1 hour accumulation above 100mm, late afternoon on 4 th October. As a consequence, the community of Schoelcher was very rapidly flooded; - 24 December 2010 : A strong convective burst in a pseudofrontal system gave 160mm in three hours over a very small region of the north-atlantic coast; (24 hours accumulation above 240mm was recorded on automated rain gauges); Flash flooding in Sainte-Marie forced people to evacuate on Christmas Eve.