Tropical Update (8/21/2011)

Figure 1. Infrared satellite imagery of Atlantic Basin.

There are 3 systems in the Atlantic Basin, currently:  the remnants of Harvey, Tropical Storm Irene, and a weak tropical wave west of the Cape Verde Islands.

Remnants of Harvey

Harvey is now just a remnant low pressure area in the southern part of Mexico.  Here is the latest from Harvey as of 10:00 am CDT:

LOCATION...17.7N 92.6W
ABOUT 125 MI...200 KM ESE OF COATZACOALCOS MEXICO
MAXIMUM SUSTAINED WINDS...30 MPH...45 KM/H
PRESENT MOVEMENT...W OR 275 DEGREES AT 13 MPH...20 KM/H
MINIMUM CENTRAL PRESSURE...1006 MB...29.71 INCHES

Harvey will continue moving in a west-northwestward motion until it dissipates sometime in the next 24-36 hours.  It could intensify some if its center enters the extreme tip of the Bay of Campeche.

Figure 2. NHC's forecast track of Tropical Cyclone Harvey.

Tropical Storm Irene

This is the storm that everyone living on the east coast of the U.S. should be monitoring, including the state of Florida.  Irene will likely affect most of the east coast, (no matter where it makes landfall) producing heavy rain and gusty winds.  Irene became a tropical storm sometime yesterday afternoon, after a recon airplane found circulation near the surface of the storm.  Here is the latest from the National Hurricane Center, as of 2:00 pm AST:

LOCATION...17.5N 63.7W
ABOUT 70 MILES...115 KM...ESE OF ST CROIX
ABOUT 185 MI...300 KM ESE OF PONCE PUERTO RICO
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 18 MPH...30 KM/H
MINIMUM CENTRAL PRESSURE...999 MB...29.50 INCHES

There is a high probability that Irene will become the first Hurricane in the 2011 Atlantic hurricane season, and possibly the first hurricane to strike the United States since Hurricane Ike in 2008.

Hurricane warnings have already been issued for the entire Puerto Rico coastline and for much of the Dominican Republic eastern and southern coastline.  Full map of watches/warnings below.

Computer forecast models are still in agreement that a hurricane will form, but are struggling on how intense and the exact track that Irene will take.   A mid-level subtropical ridge in the western Atlantic will determine its path.  A weaker ridge will drive it more easterly and towards the east coast of Florida/Georgia/South Carolina coast.  A stronger ridge would keep it more on a southerly and westerly track and might affect the west coast of Florida.  The forecast calls for a couple of mid-level troughs that will be sweeping through the eastern U.S. that might weaken the ridge by mid-week.  We’ll have to see how these troughs affect the mid-level ridge.

The National Hurricane Center still splits the difference between the extremes of the computer models.  They still have the path hitting southern Florida as a Category 1 or weak Category 2 hurricane.

Figure 3. NHC's forecast path of Irene. This map also shows all of the hurricane watches/warnings and tropical storm watches/warnings.

Figure 4. One computer forecast model (12Z GFDL) tracking Irene towards the west coast of FL. Forecast Hour = 126.

Figure 5. Another computer forecast model (12Z HWRF) tracking Irene towards the SC border. Forecast Hour = 126

Figure 6. 12Z Spaghetti plot of statistical forecast models of Irene.

Invest 98

This tropical wave doesn’t look like it will affect the United States, but it is still worth monitoring.  Right now, it is surrounded by dry air and strong shear, struggling to organize as a storm.  NHC has a 10% chance of organizing into a tropical cyclone in the next 24-48 hours.  If it were to organize, its movement would be northwestward.

Figure 7. Spaghetti plot of invest 98.

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About Brian

University of Oklahoma graduate with a degree in Meteorology. Follow me on Twitter: @WeatherInformer
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