Thursday, August 25, 2011

More than a Tempest in a Teapot -OR- Hurricane Irene Update (Part 1)

The MODIS Instrument aboard NASA's Terra satellite captured this visible image of Hurricane Irene over the southern Bahamas on August 24, 2011 at 15:05 UTC (11:05 a.m. EDT) as the storm was about to cross over Crooked Island in the Bahamas.

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OK, it's time to start talking about Hurricane Irene and what may happen this weekend.

First up, my planned beach weekend to Wildwood, New Jersey with Gary and Larry has been postponed until Sept. 9th - 12th, so I will be in D.C. during the storm.

NHC Hurricane Irene 5-day track issued at 5PM EDT, Aug. 25, 2011, source here. Of note, D.C. itself is under a tropical storm watch

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Secondly, the current forecasted track of Irene -- after marching steadily eastward over several day s-- has moved back to the west and is now on a path that would take it directly up the Eastern Seaboard from a landfall between Cape Fear and Cape Outlook -- and in particular, Topsail Beach and Emerald Isle -- to just off Ocean City, Md./Rehoboth Beach, Del., and then along the Jersey shore (!) with another landfall DIRECTLY OVER New York City or just east of it, and thence north into New England.

The two tropical guidance models -- the GHM and HWRF -- have shown somewhat different paths the 12UTC GFDL Hurricane Model (GHM) showing the storm passing RIGHT OVER D.C.

The GFDL Hurricane Model (GHM) 12UTC 25 Aug. 2011 run showing mean sea-level pressure (MSLP) and 6hr precipitation valid at hour 78 (18UTC 28 Aug. 2011). The GHM shows the center of the low right over D.C.

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However, the most recent runs of the Hurricane Weather Research Forecast (HWRF) model and the main weather operational models -- the GFS and the NAM -- show the track running along the coast.

The 18Z GFS 25 Aug. 2011 showing MSLP and 850mb temps along with 6 hour precipitation valid at hour 60 or 6Z 28 Aug. 2011.

Long story short, Hurricane Irene at the synoptic scale is sandwiched between a ridge over the Western United States and the summertime semi-permanent Bermuda-Azores high, the hurricane will follow an exact track that will be determined by the most minor of shortwave impulses (as shown in the 500mb flow) over Canada.

In terms of strength, the forecast does not call for any significant strengthening but rather to remain about a medium category 3 (that's powerful enough) with top sustained winds of 115 to 120MPH.

The current top sustained wind speed is put at 115MPH (it may be a bit less) and the central pressure is 950mb. Forward motion is NNW at 14MPH. The storm center is presently at 27.0N / 77.3W or 575 miles south of Cape Hatteras, North Carolina.

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The GOES Atlantic Floater 2 image showing Hurricane Irene in visible light at 2215UTC (6:15PM EDT) Aug. 25, 2011.

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A direct strike of a category 3 hurricane on New York City would produce widespread structural damage and catastrophic flooding.  Fortunately, New York City doesn't "occupy" a huge geographic space so a direct hit is unlikely.  I am worried about the extended stretch of the Jersey shore though.

Additional updates will be forthcoming.

--Regulus

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