Tropical storm threatens to develop, could track into Gulf of Mexico

Visiable satellite image from 8:45am EDT.  The approximate center of the disturbance is marked with a red L.

Visible satellite image from 8:45 a.m. ET. The center of the disturbance is marked with a red L.

There’s a good chance area of thunderstorms in the Atlantic could organize into the fourth tropical cyclone and the third named storm of the 2014 hurricane season. On Wednesday morning, the National Hurricane Center was giving this area a 50 percent chance of developing over the next five days.

Weather models are in good agreement that Tropical Storm Cristobal (pronounced krees-TOH-bahl) will form from this disturbance and track through the northern Caribbean as a weak and disorganized storm.  Beyond that, there might not even be a storm left. But it’s also possible that we’ll be looking at a strengthening storm entering the Gulf of Mexico in a week.  Either scenario is possible, so for now, we have the luxury of time to wait and watch.

This morning, the sloppy-looking disturbance is centered 550 miles east of Trinidad and moving northwest at about 12 mph.  The central surface pressure is down to 1009 mb. This area of thunderstorms is an easterly wave that left the African coast back on August 11, and over the past nine days, it has battled with wind shear and very dry air but is now getting closer to more hospitable conditions as it nears the Caribbean Sea.  So far this season, both Tropical Depression Two and Hurricane Bertha formed from easterly waves in the deep tropical Atlantic.

Tracks of past tropical cyclones (1851-2013) that passed through the central Lesser Antilles as tropical storms during August.  (NOAA)

Tracks of past tropical cyclones (1851-2013) that passed through the central Lesser Antilles as tropical storms during August. (NOAA)

Historically, systems that pass through the central Lesser Antilles as a tropical storm during August have a wide range of outcomes, both in terms of track and intensity.  Tracks span from Mexico to New England, and intensities span from tropical depression to Category 4 hurricane, so there’s no clear climatological guide.

In the four to six day range, if the disturbance tracks over Hispaniola and Cuba, its chances of becoming a significant storm would be diminished.  But if it stays over water instead, it would almost certainly be a stronger storm since the sea surface temperature in the Caribbean is very warm, and the wind shear, which is detrimental to hurricanes, is expected to be low to moderate.  The GFS model has been consistently bringing this system into the Gulf next week, and this morning’s run continues that trend. Many other models agree, though they differ in the amount of time spent over the islands of the Greater Antilles.

Forecast tracks from three global models and four regional hurricane models. (U.Albany)

Forecast tracks from three global models and four regional hurricane models. (U.Albany)

Below is an uncanny forecast from GFS valid on the morning of the 29th: exactly on the 9-year anniversary of Katrina’s infamous landfall in the same location.

9-day forecast from this morning's GFS model run (valid on the morning of Aug 29).  Though not very intense in this forecast, the position is identical to Hurricane Katrina on the morning of Aug 29, 2005.  (WeatherUnderground)

Ninth day forecast from this morning’s GFS model run (valid on the morning of Aug 29). Though not very intense in this forecast, the position is identical to Hurricane Katrina on the morning of Aug 29, 2005. (WeatherUnderground)

In terms of overall activity, the Atlantic is close to average for this point in the season.  Using Accumulated Cyclone Energy (ACE) as a metric, the average value by this date is 18 (units are 104 knots2), and this season we’re at 14.3.  While that’s just 79 percent of average, 4 ACE units is not very significant in an absolute sense.  Using the National Hurricane Center’s climatology of seasonal storm counts, the third tropical storm normally forms by August 13th, and the third hurricane forms by September 9th.  If Cristobal forms and becomes a hurricane, it will fit nicely into an “average” season.

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