Author Topic: Atlantic Hurricane Season 06  (Read 6626 times)

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Offline John Allen

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Atlantic Hurricane Season 06
« on: 26 September 2006, 07:59:38 PM »
Considering the sad state of affairs for this season, this will be a summary and an attempt to look at reasons for the difference in season behaviour. Explanations on your part are welcome.

Season 06

Unlike the previous season(which saw 2 storms in the month of June, and generally and earlier season),
This year only Tropical Storm Alberto formed, most likely due to the penetration of Saharan dry air and heinous windshear over tropical waves entering the atlantic. Alberto formed from a tropical wave near the Yucatan penisula, and travelled NEward towards the Florida Penisula, impacting the panhandle. It approached  hurricane strength over the warm waters of the gulf(SSTs in the range 26-27degrees centigrade), however the shear enviroment held development back, and the system disapated after landfall.

This is not an unusual event: out of the last 50 years, 29 have had a tropical system in June. The lack of formation is probably due to it being the start of summer(SSTs too low to support formation in high shear enviros). Generally formation during this month is within the carribbean, as it has a warmer temperature profile.


Now this month proved to behave a bit differently to the hyperactive season of 05. In 05 , 5 Tropical systems occured with three being full blown hurricanes. Not only this, Dennis achieved category 4 status, which is a very rare event this early in the season and Emily became the only ever recorded Category 5 in July. Conversely for 06, A single lone tropical storm(and a weak one at that) formed during the middle of the month off the East US coast. Beryl had little to no interaction with the continent(except Nova Scotia), and never really got going: peak intensity occuring as Extratroppical transition was occuring.

This was slightly puzzling for a July period.  What seemed to be the main problem is warm conditions in the Saharan produces huge amounts of dust particles within the airstream moving off africa as tropical waves formed. This together with significant shear due to the presence of a subtropical trough near the middle of the atlantic, meant that any system that did form weakened significantly, and in many cases disapated halfway accross the atlantic. Shear conditions possibly related to the apparent breakdown of the Walker circulation(El Nino) may have caused the drought of development over the Carribean. However significant formation was occuring in the Eastern Pacific: again suggestion the return of El Nino.

August was the remembered month of 05, With 2 Hurricanes and 3 storms: Katrina being the star attraction Category 5.

In contrast 06 was basically a writeoff. Two TS and 1 Rather weak Hurricane showed that conditions accross the Atlantic were rather insipid to say the least.

Tropical Storm Chris formed close to the leeward islands from a tropical wave, and although promising for a while with high SST and acceptable shear,the unexpected arrival  a cold-front and associated baroclinic features really stuffed around with the circulation. An upper level low also interacted, shearing the system heavily before it could reach Cuba, and removing convection from the circulation. Peak winds were in the order of 65 MPH.

Tropical Storm Debbie looked like the Cape Verde bug was about to strike again. The system reached tropical storm strength barely 24 hours out of africa, and was steered to the NW. Southerly shear (ML Low ) restricted the system to 50 MPH, and then the remains of the circulation were collected by a Cold front.

 Hurricane Ernesto was very promising, although the forecasters struggled, with the forecast track changing from intially New Orleans impact to Haiti, Cuba and Florida. The storm was in an enviroment of weak steering currents, together with high SSTs and little or no shear. It formed from a tropical wave passing the southern leeward isles. Intial intensification was slow, with moderate shear from a departing upper level low. Rapid intensification followed together with self steering and the system became a hurricane, however interaction with Haiti, Cuba and Florida destroyed any chances of a powerful hurricane, despite the favourable enviroment. The system moved NE from florida reaching near hurricane strength before making landfall again on North carolina's coast, and raining on the US open Tennis. The system was asbsorbed by a larger ET low.

August really raises some questions about what is going on with the season: SSTs continue to rise, however the subtropical boundary seems to have remained extended quite far south for this time of year. Shear enviroments meant that many possibly waves had no chance to form any sort of a circulation before being blown apart. Further Evidence for the El Nino argument. Dry air entrainment seems to also have remained a problem in the East atlantic.

To be continued.
Explosive events coming to a weather system near you.