Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 8:55 PM GMT on August 24, 2011
Hurricane Irene remains a powerful category 3 this afternoon, with maximum sustained winds of 120 mph. Irene is moving northwest through the Bahamas at 12 mph, and its center has cleared the northern edge of Crooked Island. The next islands in the path of Irene are Rum Cay (population 80) and Cat Island (population 1700), which it will encounter later tonight. Irene will track northeast of Long Island (in the Bahamas) over the next 24 hours. George Town has been reporting wind gusts up to around 40 mph this afternoon, and wind speed will likely increase during the next 12 hours as Irene's center passes about 30-40 miles to their northeast. Long Island in the Bahamas will likely see category 1 winds, which begin at 74 mph. Shelters on New Providence and Grand Bahama are open and ready for business, and Grand Bahama International Airport will remain closed until Irene passes.
Irene continues to look well-organized on satellite, especially compared to yesterday afternoon. Since then, intense upward motion, and therefore strong thunderstorm activity, has encompassed the center on all sides, which has led to a well-defined eye. Throughout the morning, Irene's eye wall has shrunk, and a new eye wall could be developing, although it remains unclear at this point. If this is the case, it could lead to some temporary weakening of the hurricane, which would be good for the Bahamas. This afternoon, Irene's hurricane-force winds extend 50 miles from the center, and tropical storm-force winds extend up to 205 miles from the center. Earlier this morning, an Air Force Hurricane Hunter mission investigated Irene and a NOAA Gulfstream (Gonzo) is currently collecting data around the hurricane.
Figure 1. Microwave satellite imagery of Irene captured at 8am this morning. Image source: Naval Research Laboratory.
Track forecast for Irene
NOAA has continued dropsonde missions today, scouring the atmosphere for data as far north as the waters off of South Carolina. Every bit of upper-air data that the models can ingest will lead to better forecasts and decreased uncertainty. These missions are an investment that pay off. Irene will track through the central Bahamas today, the northwestern Bahamas on Thursday, and approach the Outer Banks of North Carolina on Friday. Beyond this there is a bit of divergence in the models. Both the GFDL and the HWRF are forecasting a landfall on Long Island, New York, and the ECMWF continues to suggest a landfall even further west than that. NOGAPS is still the eastern outlier, which misses the U.S. all together and makes landfall in Canada. Today the official track forecast from the National Hurricane Center agrees with the GFS forecast through Saturday morning, and then diverges ever so slightly to the west of that through Monday. It has become clear over the past 3 days that everyone on the East Coast from North Carolina to Maine should be prepared to feel impacts from Hurricane Irene.
Figure 2. Official track forecast provided by the National Hurricane Center.
Intensity forecast for Irene
Irene continues to be embedded in a large envelope of moisture, and wind shear is expected to remain low to moderate, 5 - 20 knots, for the next three days. With water temperatures very warm, 28 - 30°C, these conditions should allow for intensification to a category 4 hurricane (winds of 131 to 155 mph). The only reliable model that's not forecasting this intensification is the GFS, and this is likely due to its relatively course spatial resolution. The National Hurricane Center expects Irene to intensify to a category 4 tomorrow, with a decrease in intensity back to a category 3 on Friday.
For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, check out the NHC wind probability product.
Wunderground has detailed storm surge maps for the U.S. coast.
Our Wundermap is also a great resource for tracking hurricanes, with the ability to turn on multiple layers of data, including satellite, official track forecast, and current weather observations from not only the U.S. but the Caribbean and Bahamas, as well. Here's a link to get you started.
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