WRAL WeatherCenter Blog


Posted August 17, 2009

Three named Atlantic tropical cyclones in one weekend, that is! Just last week I posted here about this being the deepest we'd gotten into the tropical season here since 1992 without a named storm, mentioning that there were a couple of systems out there that looked as if they could prevent us from tying that record. Of course, we're nowhere close to the older record for the latest tropical storm I mentioned in that same note, September 15th back in 1914.

We ended up coming within a single day of the 1992 mark. That year, the first named system formed on August 16th. This year, we still had no such systems on the map as of early morning on the 15th, but by later in the day we had two, and by Sunday afternoon Ana, Bill and Claudette were all roaming across various parts of the Atlantic basin.

Since then, Ana has weakened to a tropical depression and appears in danger of becoming even more disorganized in the coming days as it interacts with Hispaniola and Cuba, perhaps being reduced to a remnant low or even an barely detectable wave. Claudette has already lifted out of the eastern Gulf of Mexico, making landfall just after 1 am this morning along the Florida panhandle just southeast of Ft Walton Beach, as more of a heavy rain producer than a serious wind problem (sustained winds at Florida coastal stations ran in the upper 20s to mid 30s, with gusts as high as 46 mph at Apalachicola, 44 mph at Destin and 41 mph at Tyndall AFB), and it appears most of it's deep moisture will end up passing by west of our state.

Bill, on the other hand, is a storm that we've mentioned for about a week as looking more impressive in computer model projections, and it has now reached minimal hurricane status, with the National Hurricane Center forecasting a continued increase in intensity, with some potential for becoming a Category 3 or 4 storm over the next few days. Early long range outlooks for this storm indicated a threat to the southeastern U.S., but over the past two to three days projections have become rather consistent with a turn to the north well out to sea, with the center passing near or even east of Bermuda early this weekend.

Sometimes when steering patterns are weak or ill-defined, a number of computer models will disagree substantially with their handling of such a storm, but for now the main variation is with forward speed. I've attached four 120-hour forecasts captured from the Penn State University "e-wall" models site, showing their sea level pressure and low level vorticity patterns for this Friday evening at 8 pm. The four models are the National Weather Service's Global Forecast System (GFS), a Canadian Meteorological Centre model (CMC), a Navy model called NOGAPS, and the European Center for Medium Range Weather Forecasting (ECMWF) model. At the time shown, all the models have Bill moving on a path more or less directly toward the north along the west side of a large subtropical high pressure ridge. The positions are pretty similar, with the ECMWF and GFS a little farther along toward the north by then as compared to the other two models.

If they are all reasonably on target, there will be little or no impact from the storm on our state beyond perhaps some notable swells from the east. Of course, it's still a little soon to have total confidence in that, so we'll all want to stay tuned...


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