Tropical Storm Sean Threatens (Advisory #4)


“…SEAN MOVING SLOWLY WESTWARD WITH NO CHANGE IN STRENGTH…

SUMMARY OF 1000 PM EST…0300 UTC…INFORMATION
———————————————–
LOCATION…27.9N 70.1W
ABOUT 440 MI…705 KM SW OF BERMUDA
MAXIMUM SUSTAINED WINDS…50 MPH…85 KM/H
PRESENT MOVEMENT…W OR 270 DEGREES AT 3 MPH…6 KM/H
MINIMUM CENTRAL PRESSURE…999 MB…29.50 INCHES” – NHC

Bermuda is under a Tropical Storm Watch for potential impacts from Tropical Storm Sean. Recently formed Tropical Storm Sean was initially a sub-tropical storm, but gained sufficient tropical characteristics to be classed as a tropical storm. Some strengthening is expected before it starts to transition into a post-tropical cyclone. Sean is a large storm and is likely to bring tropicals torm force winds to Bermuda. This is the main difference between Sean and the many other systems that came close to Bermuda in the past few years – size.

Tropical Storm force winds extend out over 200 miles from the center, but mainly in the squally spiral bands. Sean is expected to pass between 50 and 100 miles to the west of Bermuda Friday morning, but tropical storm impacts could occur as early as Thursday. Being in the right front quadrant, and the dynamic atmosphere there with a fall atmosphere in place, tornadic squalls are possible or even likely if bands set up over Bermuda, this would mean a potential closure of the Causeway and the Airport.

However, it is too early to determine specific impacts from Sean as there is still uncertainty as to the way systems react to changing atmospheric conditions when they transition from extra-tropical, to sub-tropical, to tropical cyclones. Therefore there is a higher than normal degree of uncertainty in the future structure and therefor strength of Sean. Those two factors determine the impacts the storm will have on land, if any.
We do know for sure, that the winds will remain strong until the storm dissipates as a pressure gradient between strong high pressure to the north and Sean’s low pressure to the south west continues to exist. Further shower activity is likely to persist as well as their is significant convergence in this area of the high pressure system, and the low pressure system, these may produce thunder and lightning at times – beware.

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