A Memorial Day Weekend Tropical System For the Southeast U.S.?
We're fast approaching the official June 1 start of the Atlantic hurricane season, and we already have an area of concern to watch for possible genesis of a tropical depression during the coming Memorial Day weekend. An area of low pressure is expected to form on Friday near to or a few hundred miles north of the Bahama Islands, and this low has the potential for tropical development as it moves northwest towards the Southeast U.S. coast. Sea Surface Temperatures (SSTs) over the Bahamas are about 28 - 29°C (82 - 84°F), which is 1 - 2°C (1.8 - 3.6°F) above average. These waters are plenty warm enough to support formation of a tropical storm. Phase space diagrams from Florida State University have been consistently showing that this storm will be a symmetric warm core system, which is technical lingo for a storm that is tropical in nature, rather than subtropical or extratropical.
Figure 1. Departure of Sea Surface Temperature (SST) from average for May 24, 2016. The Bahamas had SSTs that were 28 - 29°C (82 - 84°F), which is 1 - 2°C (1.8 - 3.6°F) above average. Image credit: tropicaltidbits.com.
Figure 2. Surface pressure (black contours) and 6-hour precipitation (in mm/hr) predicted for Saturday, May 28, 2016 at 2 am EDT (06Z) from the 8 am EDT (12Z) Tuesday, May 24 run of the GFS model. An area of low pressure with the potential to develop into a tropical depression was predicted to be near the coast of South Carolina. Image credit: tropicaltidbits.com.
What the models say: a heavy rain threat for the Southeast U.S. coast
In my 2013 blog post, Genesis of New Atlantic Tropical Cyclones: Which Model Should You Trust?, I explained that we have three models that have proven to be fairly reliable for predicting the genesis of tropical depressions up to four days in advance: the American GFS model, the European ECMWF model, and the British UKMET model. Over the past two days, the GFS and European models have been showing the potential for a tropical depression to form near or to the north of the Bahamas; the UKMET model has merely shown a tropical disturbance forming. The models have widely differing ideas on how much wind shear might be present, so it is too early to say if this weekend's system is a legitimate threat to develop into a tropical depression. The main concern for this weekend's low will be heavy rain over the northwest Bahamas and the Southeast U.S. coast, as the storm likely will not have enough time over water to become a strong tropical storm or hurricane. The GFS model is indicating a possible threat to the coasts of northern Florida, Georgia, or South Carolina early next week, while the European model takes the low farther to the north, to the coast of South Carolina or North Carolina. I'll keep you updated each day this week with the latest prognosis for this potential early-season storm. Should the storm over-achieve and become a tropical storm, it would be named Bonnie.
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Dr. Masters® co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather
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