Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 22. syyskuuta 2011 klo 13:42 (GMT)
Tropical Storm Ophelia passed just south of buoy 41041 early this morning, and the sustained winds of 60 mph measured at the buoy were a bit of a surprise, given the storm's sheared appearance on satellite imagery. Ophelia is showing the classic appearance of a tropical storm experiencing high wind shear. The low level center of circulation is exposed to view, and the storm's heavy thunderstorms have been pushed to the northeast side of the center of circulation. An analysis from the University of Wisconsin CIMMS group shows a high 20 - 25 knots of wind shear due to strong upper level southwesterly winds. Water vapor satellite images show a large area of dry air to the the west of Ophelia, and the strong upper level west-southwesterly winds bringing high wind shear to the storm are also injecting dry air into the storm's core, interfering with development. Ophelia will be passing north of buoy 41040 Friday morning, and the Hurricane Hunters will be making their first flight into Ophelia on Friday morning.
Figure 1. Morning satellite image of Ophelia showing the low-level center exposed to view, with all the storm's heavy thunderstorms pushed to the northeast side.
Forecast for Ophelia
The latest SHIPS model forecast predicts that Ophelia will experience moderate to high wind shear of 10 - 25 knots over the next five days, and will move into a region with drier air. The combination of shear and dry air should keep Ophelia from strengthening, and is likely to weaken the storm. However, the models have backed off on calling for outright dissipation of Ophelia this weekend, as some were calling for in their runs yesterday. Ophelia is having some trouble disentangling itself from a band of heavy thunderstorms to its south, associated with the Intertropical Convergence Zone (ITCZ). This has likely kept the storm a little to the south of the expected track. Ophelia should begin moving more to the northwest by Friday, when the ridge of high pressure steering it westwards weakens. This should make the core of the storm miss the Northern Lesser Antilles. These islands could see some wind gusts of 30 - 40 mph and a few heavy rain squalls from Ophelia on Sunday, but the islands will be on Ophelia's weaker (dry) side, limiting the potential for adverse weather. At longer ranges, Ophelia may pass close to Bermuda as early as Wednesday, since a large cut-off low pressure system over the Eastern U.S. should turn Ophelia to the northwest and then north early next week. Ophelia may eventually be a threat to Canada, but it is too early to assess the odds of this happening.
Elsewhere in the tropics
In the Eastern Pacific, Tropical Storm Hilary is expected to intensify into a hurricane and bring heavy rains of 3 - 5 inches to coastal Mexico as the storm moves parallel to the coast, about 150 miles offshore. Hilary may turn north and affect Baja 7 - 10 days now, but it is too early to lay odds on this. In the far eastern Atlantic, a tropical wave that emerged from the coast of Africa this morning is predicted by the GFS and NOGAPS models to develop into a tropical depression early next week. Steering currents favor a west-northwest to northwest track early next week for this disturbance.
Figure 2. NASA posted a spectacular movie yesterday of the Aurora Australis taken by the International Space Station. The rippling green curtains of the aurora as the space station zooms overhead are amazing!
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