Hurricane Bill

Pre-Landfall 1 | Summary
Posting Date: August 17, 2009, 11:07:00 AM

Hurricane Bill, the first Atlantic hurricane of 2009, formed early Monday morning after an unusually quiet start to the Atlantic tropical cyclone season. Bill is expected to continue to strengthen, possibly becoming a major hurricane (with sustained winds of over 110 mph) by Wednesday. Meanwhile, Tropical Depression Ana, which had weakened from tropical storm status, is currently moving west-northwest through the Caribbean islands. Ana is forecast to dissipate today and is not expected to pose a threat to the United States. A third system, Tropical Depression Claudette, formed quickly in the Gulf on Sunday morning and made landfall less than 12 hours later at tropical storm strength along the Florida Panhandle. Claudette continues to weaken as it moves northwest over Alabama, bringing heavy rains; it is not expected to cause significant wind or flood damage. Per the National Hurricane Center’s 11:00 AM EDT advisory today, Hurricane Bill is located 1080 miles east of the Lesser Antilles and is moving west-northwest at a forward speed of 16 mph. According to satellite imagery, Bill does not yet display an eye, but the core of the storm is showing signs of increasing organization and several well defined bands of heavy thunderstorm activity are present. With a minimum central pressure of 977 mb and maximum sustained winds of about 90 mph, Bill’s radius of hurricane force winds extend 30 miles from its center, and tropical storm force winds extend 145 miles. Wind shear along Bill’s track is expected to be low for the next three days and sea surface temperatures, currently around 27°C (80°F), are warm enough to support continued intensification. The NHC forecasts that Bill will strengthen to a major Category 3 or Category 4 hurricane by Wednesday, but increasing shear thereafter will likely prevent further intensification. The Bermuda high will continue to steer Bill on a northwesterly track for the next several days, after which a major trough of low pressure is expected to curve Bill in an increasingly northern direction. As a result, hurricane force winds should remain well clear of the Caribbean islands. It is too early to forecast how Bill will impact the east coast, although it is currently not expected to make landfall in the U.S. A more immediate concern is how Bill will affect Bermuda on Saturday, since many models expect Bill to pass within 200 miles of the island.

Three Day Track Forecast for Hurricane Bill. (Source: NHC)

Tropical Depression Ana, weakened by a dry embedded Saharan Air Layer, is becoming increasingly disorganized as it approaches landfall in Puerto Rico. According to the NHC’s 11:00 AM EDT advisory, Ana is located 75 miles south of San Juan, Puerto Rico, and packs maximum sustained winds of 35 mph. While Ana is bringing heavy rains, its fast forward speed of 28 mph will likely mitigate the possibility of flooding. Total expected accumulation is 2 to 4 inches in most locations, and up to 6 inches in isolated mountainous pockets. A tropical storm watch remains in effect for Puerto Rico, the U.S. Virgin Islands, the British Virgin Islands, and parts of the Dominican Republic. Ana is expected to dissipate as it moves overland through the rough mountainous terrain of Hispaniola.

High wind shear, the difference in wind speed at different heights, is destructive to hurricane formation. The absence of strong wind shear in Hurricane Bill’s path is expected to help the storm intensify. (Source: AIR)

Finally, Claudette, currently a tropical depression with maximum sustained winds of 35 mph, made landfall early Monday morning at 1:15 AM EDT near Fort Walton Beach, Florida, with maximum sustained winds of 50 mph. As of the NHC’s final advisory for the storm, issued at 10:00 AM EDT, Claudette was located 85 miles southwest of Montgomery, Alabama and was moving northwest at 12 mph. It is forecast to curve north-northwest later today across southwestern Alabama and into northeastern Mississippi. Expected rainfall is 3 to 6 inches in most areas, and up to 10 inches in isolated pockets. Inland flooding is a possibility, but no major damage is expected. The figure below shows sea surface temperature (SST) anomalies and whole field contours. As expected, all three storms have developed in a region of ocean temperatures of greater than 26.5°C (80°F), the threshold for tropical cyclone formation.

The black line in each storm's path shows where the storm has tracked, while the colored segment following the black line indicates the forecast track, as given by the NHC. Bright orange indicates warmer than usual ocean waters. (Source: AIR)

The AIR tropical cyclone team continues to monitor these tropical systems and will provide updates as warranted.

Pre-Landfall 1 | Downloads
Posting Date: August 17, 2009, 11:07:00 AM