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Special Weather Summary For Tropical Storm Danny, Thursday, August 27, 2009
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Tropical Storm Danny has an impressive circulation, but its array of convection is chaotic and it is a stretch to call the circulation a tropical storm, at least for now. Danny is heading due westward (not northwest as some have maintained), and the model forecasts for this disturbance have so far not verified. The reason for the poor performance of the equations is simple: none acknowledge the disorganization of the low, nor do any of the schemes have a handle on the three key features which will shape the future of the storm: the strong heat ridge over the north central Atlantic Ocean (which may retrogress a bit), the TUTT signature over the Deep South, and the digging polar shortwave across the Upper Midwest. As Danny comes into contact with these systems, I believe that the character, strength, and impacts from this impulse will change, perhaps dramatically.
On Friday, Danny will begin to interact with the upper low over Dixie, which itself will be blending in with the stronger cold trough complex taking shape over the Great Lakes. The addition of cyclonic energy and upper difluence over a warm water body will make for a period of strengthening, perhaps to Category 1 hurricane status. However, the sheared look of the tropical cyclone will not really go away, and an inverted trough may begin to take shape over NC as Danny draws near Cape Fear NC. Thunderstorms ahead of the cP cold front may by themselves be severe as the boundary pushes through the Ohio and Tennessee Valleys into Appalachia. On Friday night, convection associated with Danny and the TUTT signature should begin to fire in an arc to the northwest of the low pressure center, which will turn north as the center becomes sandwiched between the subtropical high to its northeast and the neutral tilt trough complex that arises form the merger of the two cyclonic distortions. It is still entirely possible that Danny may track directly along the Mid-Atlantic shoreline or just inland. For now, a path about 50 - 75 miles offshore is probably a safe bet, as is rainfall amounts of 1 to 3 inches along and to the right of Interstate 95 from Richmond VA to New York NY. Local spikes to 5 or even 6 inches of rain are probable if the low center takes a leftward variation of the track scenario. Some coastal flooding is probably a given, and local wind gusts may exceed 50 mph in spots by daybreak on Saturday, when the combinant Danny system should be nearing Islip LI NY.
I believe that Danny will link or phase with the TUTT and full-latitude trough on the morning of August 29, A path of the vestigial center, replete with some stronger wind gusts, will be from eastern Long Island NY into the Boston MA metro by Saturday evening. Acceleration of the Danny-related low and the former primary cyclone should occur Saturday night, with the greatest pressure falls into the Bay of Fundy on Sunday and then to about Gander Newfoundland on early Monday morning. Gusty, rather cool winds will take over most of Appalachia and the Northeast to the rear of Danny, with the polar air mass actually reaching the Gulf of Mexico and Florida Peninsula by the night of August 31.
In summary:
Top winds of Danny: 70 mph before graze or landfall just north of Cape Fear NC; most speeds 35 - 50 mph through the remainder of its lifetime.
Rainfall forecast: highest amounts of 1 to 3 inches along and east of Interstate 95 between Richmond VA and New York NY; QPF of 3 - 6 inches possible in LI NY; S CT; RI; E MA and again in NS
NASA
NASA
NOAA
NOAA/NCEP
Colorado State University
Colorado State University
Plymouth State University Weather Server
WEATHERAmerica
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