Towers Perrin Hurricane Blog

Tropical Storm Danny has begun its northward motion based on the latest reconnaissance.  Winds have dipped in many areas of the storm, however one region did record sustained winds of 40-45 mph, thus holding on to the “tropical storm” designation.

Danny may strengthen slightly as it moves under an area of moderate upper level convergence over the next 24 hours.  However the system will then encounter strong shear associated with a surface front measuring around 35 knots, which will eventually convert Danny to an extra-tropical system at roughly 36 hours.

The chance of the east coast experiencing sustained tropical storm forced winds (35+ mph) is relatively low at this time. 

You can see from the image below from Wunderblog just how much the storm has struggled with the shear affecting the convection.  The areas of heaviest activity are well east of the central rotation, which has caused multiple reformations thus far.

Tropical Storm Danny continues to exhibit strange behavior and shape, but aircraft recon is still recording sustained winds around 40 mph in the strongest quadrants to the East of the low pressure center.   Significant wind shear has kept most of the convection from forming around the low and hindered possible strengthening overnight.

Danny will encounter an upper level ridge which should provide enough stability to increase winds to 50 mph over the next 24 hours.  However a deep surface trough will begin to overtake the storm and its forward, or rather northeastward motion will pick up speed.

Tropical Storm Watches remain in effect for the Outer Banks, but the probability of experiencing TS winds is relatively low at 20-30%.  The TS wind speed probabilities for Cape Hatteras have decreased a bit as well for the weekend.  Rip tides will again be present, though the wave activity is not as large as Bill, which was a strong Cat-2 (and growing) at a similar latitude last week.

GOES Floater 090828 1145UTC

The most recent hurricane aircraft recon has indicated that the winds from Tropical Storm Danny have become somewhat better organized in the western front.  However the overall max sustained winds have weakened slightly to 50 mph. 

Satellite imagery shows a strong presence of dry air to the west of the system.  This will hold Danny’s intensity steady over the next 24 hours.  The system will then unite with an upper level high which will provide a small window for potential strengthening in 24 – 36 hours.

Although some models are in disagreement, most do not predict Danny to reach hurricane strength. 

The NHC forecast track has not changed significantly, and Tropical Storm Watches have been issued for the Outer Banks of NC.  The forecast still brings Danny to Cape Hatteras late Saturday afternoon.

Water Vapor Image  -click for loop-

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The latest guidance from the NHC shows Bill has weakened slightly to a strong Cat-2 hurricane after encountering some moderate shear.  There is a good chance the system will reorganize as shear diminishes and hits warmer waters Friday.  However the forecast shows Bill slowing to a weak Cat-2/strong Cat-1 as Saturday progresses.

The forecast models are in good agreement on the track, taking Bill due North Friday night, before making a NE turn into Sunday. 

The greatest threat to the US will be in the form of coastal erosion as high seas will affect the eastern seaboard from Florida to Maine.  The highest expected seas will occur near Cape Cod, which could experience 20′ waves.  The threat from rip currents is moderate and expected to increase as Bill travels North.

We will continue to monitor the system and provide updates as necessary.

After a slow start, the 2009 Atlantic hurricane season has begun, and in grand fashion.  On Saturday the 15th, the first and second tropical systems of the season, Ana and Bill, developed.  By early Sunday morning, Claudette had strengthened from a depression to a tropical storm, and is making landfall along the Florida panhandle and Alabama coast.

The main threat from Claudette will be inland flooding, as 3 – 5 inches of precipitation are forecast with areas of heavier precip possible.  Sustained winds around 6o mph are expected, with higher gusts also present.

Ana is weakening due to a strong influence from dry Saharan air.  Organization is fading quickly and forecasters do not expect the storm to redevelop at this time.

Last, but far from least, is Tropical Storm Bill.  Bill is likely to strengthen to a hurricane overnight, and reach “intense” status by Friday afternoon.  The models are in good agreement over the next 3 days, but then diverge.  A developing low pressure system over the US is expected to develop, and may steer Bill away from land.   Model plot from Colorado State below shows the predicted tracks.  These are used for guidance only and can quickly change with each run.