Debby, the Fourth Named Storm


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National Hurricane Center Satellite Image of Post-Topical Storm Debby as a sharp trough of low pressure over the Gulf Stream. June 27th 2012 (See NHC’s Facebook page)

Tropical Storm Debby formed on Saturday, June 23rd out of a tropical mess that converged over the Yucatan Channel. A weak tropical wave merged with the monsoon trough that typically exists over Central America and was pulled northwards through the Yucatan Peninsula, Yucatan Channel, and into the Gulf of Mexico where it developed a well defined low level circulation, although detached from the deepest convection (showers and thunderstorms), and was named Tropical Storm Debby.

The storm meandered and drifted north and eventually eastwards, causing headaches for the forecasters at the National Hurricane Center. The slew of typically reliable forecast models showed the storm heading westward into Texas. However, as the storm came together, the ridge over the American mid-West was stronger than forecast and pushed further northwards into Canada, which allowed a frontal trough to dip further southwards into the Gulf of Mexico and pick up Debby and take it eastwards. So, instead of heading westward as initially forecast, Debby headed eastward towards Florida and the National Hurricane Center had to completely flip their forecast!

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National Weather Service Jacksonville, FL rainfall totals map. This shows the eastern extent of over a foot of rain in North Florida. Major flooding occurred along and south of I-10 as a result of Tropical Storm Debby’s heavy rain.

Heavy rainbands set up over Central and North Florida and dumped 12-24″ of rain along a large swath of this region. This rain eliminated any drought conditions and was so extensive that it led to historic major flooding in some regions of North Florida. Hundreds of water rescues and evacuations were carried out as a result of the major flooding. Additionally, tropical storm force winds along the coast for days generated a 2-4 foot storm surge that caused some minor coastal flooding in Florida.

Debby has since made landfall in the Big bend region of Florida as a weak Tropical Storm, weakened to a Tropical Depression, moved into the Western Atlantic and become a Post-Tropical Storm as it succumbed to the influences of the baroclinic zone along the front that steered it eastwards across Florida.

Forecast for Debby:

The Post-Tropical Storm should continue heading eastwards and start to make a turn more northeasterly Thursday evening/night. This puts the storm on a track that would have it passing dangerously close to the north of Bermuda. Although no longer a Tropical Cyclone, the impacts in terms of wind and severe thunderstorms remains the same and so Debby should be closely monitored.

Some forecast models are hinting at Debby transitioning back to a Tropical cyclone, as it moves across the warm Western Atlantic waters and into lighter wind shear. If this does occur, Watches or Warnings may be necessary for Friday afternoon in Bermuda. Although the closest point of approach may not occur until late night on Friday, Tropical storm (gale) conditions would likely extend far from the center which is what the closest point of approach is judged on.

At this time, Bermuda should expect showers and rain from tonight into Saturday. Squally weather could develop at times with a chance for thunderstorms. Strong winds, 20-30mph with gusts to 40mph or higher in and around squalls should be expected through this entire period, but higher winds may exist around the circulation of Debby if it gets close enough and/or strengthens.

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