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Subtropical Storm Beryl forms

By: Dr. Jeff Masters, 4:03 PM GMT on May 26, 2012

The second named storm of this unusually fast-starting 2012 Atlantic hurricane season is here. Subtropical Storm Beryl formed Friday night, a few hundred miles east of the South Carolina coast, from an area of disturbed weather that had moved from the Western Caribbean northeastward. Beryl's formation marks the first time since the hurricane season of 1908 that two Atlantic named storms have formed so early in the year. The only other year with two storms so early in the year was 1887. Records of tropical cyclones in the Atlantic extend back to 1851.

Figure 1. Morning satellite image of Beryl.

The clockwise flow of air around an extremely intense ridge of high pressure that is bringing record heat to the Midwest this weekend is currently driving Beryl to the southwest, and this motion is likely continue until Beryl is very close to the Georgia/Northern Florida coast on Sunday night. As I explain in my Subtropical Storm Tutorial, a subtropical storm typically has a large, cloud free center of circulation, with very heavy thunderstorm activity in a band removed at least 100 miles from the center. The difference between a subtropical storm and a tropical storm is not that important as far as the winds they can generate, but tropical storms generate more rain. A key difference between tropical and subtropical storms is that tropical systems have the potential to quickly grow into hurricanes, while subtropical storms do not. Thus, we need not be concerned about Beryl intensifying to hurricane strength while it is still subtropical. If the storm manages to build a large amount of heavy thunderstorms near its center, these thunderstorms should be able to add enough heat and moisture to the atmosphere to turn Beryl into a tropical storm. This process will be aided as Beryl passes over the warmest waters of the Gulf Stream Saturday night and Sunday morning. But as Beryl makes its likely transition to a tropical storm on Sunday afternoon and evening as it approaches the coast, the storm will move off of the warmest Gulf Stream waters into waters that are cooler (25°, 77°F), and with with lower total heat content. This will limit the storm's potential to strengthen. The 11 am Saturday wind probability advisory from NHC gave Beryl just an 8% chance of becoming a hurricane. There is a lot of dry air surrounding Beryl, thanks to an upper-level low pressure system aloft, and this will keep rainfall amounts much lower that what we would expect if Beryl was a tropical storm. Thus, flooding due to heavy rains is probably not a huge concern with this storm, particularly since the Southeast U.S. coast is under moderate to extreme drought. The 2 - 4 inches of rain expected from Beryl will not be enough to bust the drought, since the Southeast U.S. is generally suffering a rainfall deficit of 8 - 12 inches (since October 1.) Heavy rains from Beryl are not likely to begin affecting coastal South Carolina, Georgia, and Northern Florida until Sunday.

Figure 2. Moderate to exceptional drought is currently gripping the Southeast U.S.; Beryl's rains would be welcome. Image credit: U.S. Department of Agriculture.

Bud hits Mexico and dissipates
Hurricane Bud hit Mexico as a tropical depression early this morning, and has now dissipated, thanks to dry air, wind shear, and interaction with Mexico's mountainous terrain. As Bud approached Mexico on Friday, it brought tropical storm-force winds and heavy rains to the coast. Winds at Manzanillo peaked at 41 mph, with a gust to 55 mph, Friday afternoon. Thursday night at 11 pm EDT, Bud peaked at Category 3 status, with 115 mph winds, becoming the earliest Category 3 hurricane on record so early in the year in the Eastern Pacific. There are no reports of deaths or damage from Bud so far, and with only another inch or so of rain expected from the storm, Mexico appears to have escaped serious damage.

Figure 3. True-color satellite image of Hurricane Bud taken by NASA's Terra satellite at 1:15 pm EDT May 25, 2012. At the time, Bud was a Category 1 hurricane with 85 mph winds. Image credit: NASA.

Jeff Masters


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