Florida to get socked; Stan looking strong
Tropical disturbance approaching Florida
An tropical disturbance approaching the central Bahama Islands is poised to sock Florida Tuesday night and Wednesday with heavy rains and high winds. While the shear is a high 10 - 20 knots over the system today, the shear is expected to decrease to 5 - 10 knots tomorrow, accompanied by the formation of an upper-level anticyclone on top. This system has the potential to develop into a tropical depression by the time it reaches Florida, and a reconnaissance flight is scheduled for Tuesday at 11 am. The disturbance currently has no surface circulation center; the spinning clouds seen on satellite images at 25N 70W are from an upper-level low that the disturbance is now separating from. Beaches along central Florida are already suffering erosion from the large pounding waves emanating from this disturbance.
The forecast track of this disturbance is complicated by the expected interaction with a cold front forecast to move over the East Coast by the end of the week, and an upper-level low pressure system expected to form in the northern Gulf of Mexico on Wednesday. The GFS model shows the disturbance splitting into two storms, one that tracks across Southern Florida into the Gulf of Mexico, and the other which moves northward along the coast, brushing the Carolinas and New England. Neither storm has a very good chance to develop into a hurricane. Anything moving into the Gulf will encounter the upper-level low and its shearing winds. An East Coast storm would have low shear and a favorable upper-level winds for development, but not much time over warm water. Regardless, Florida is in for a very wet week with potential serious flooding problems, both from the rains of the tropical disturbance, and from the upper-level low, which is likely to entrain copious tropical moisture over the state.
Figure 1. BAMM model forecast track of Bahamas suspect area. The intensity forecast numbers from the SHIPS model are far too high; this system will be lucky to make it to tropical storm strength (40 mph winds). The GFS and NOGAPS models are tracking the upper-level low northeast of the Bahamas instead of the surface tropical wave.
Tropical Storm Stan
There have been three center penetrations of Stan this afternoon by the Hurricane Hunters, most recently at 4:50 pm EDT. The central pressure fell 6 mb in the three hours between passes, and the highest winds measured were in the 55 - 60 mph range. Satellite imagery continues to show an improving outflow pattern, larger area of deep convection near the center, and more low-level spiral banding. The chances for continued intensification are high, as Stan is over 30C waters and is positioned under a large anticyclone that will provide good outflow and wind shear values below 5 knots. Stan will probably be a Category 1 hurricane as it approaches the Mexican coast on Wednesday, and a Category 2 hurricane is not out of the question.
The 12Z ( 8am EDT) model runs continue to forecast a landfall in Mexico between Tampico and Veracruz on Wednesday. After briefly stalling this afternoon while re-organizing, Stan is moving westward again at about 6 mph under the influence of a strong ridge of high pressure. This ridge is forecast to weaken as a weak trough of low pressure swings across the U.S. and drops a cold front and upper-level low pressure system across the northern Gulf of Mexico by Thursday. In response to this weakening, Stan is expected to slow down as he approaches the coast Tuesday, but it is looking less and less likely that Stan will stall in the Gulf and wander erratically.
A low pressure system accompanied by a concentrated area of thunderstorms is halfway between Africa and the Lesser Antilles Islands, at about 14N 36W. This system is fighting significant wind shear, and will probably not develop into a tropical depression. It is expected to move northward the next five days over open waters and not threaten any land areas.
PaaMul, Yucatan Peninsula, 30 miles north of Tulum