For the past week, hurricane forecasters at the National Hurricane Center have been following the exploits of a weak tropical system as it plodded across the Caribbean Sea. During the past two days, the system has gradually strengthened and winds have increased significantly. On the east of the system, winds were already blowing at gale force (39 to 54 miles per hour) early this Thursday morning (Oct. 3, 2013). The only thing not yet in place was a well-defined center of circulation. Based on what weather satellite data was showing (a large clockwise spiral atop the developing system – Fig. 1), it was apparent that changes to system classification would happen quickly. They did!
Hurricane forecasters named Karen and upgraded her status to a 60-mile per hour tropical storm at 8:00 a.m. C.D.T. By 10:00 a.m., Karen’s winds had increased to 65 miles per hour, according to hurricane hunter aircraft data. Tropical force winds extended outward 105 miles from the center of circulation.
According to the 10:00 a.m. National Hurricane Center advisory, Karen was located at 22.2 degrees North latitude and 87.9 degrees West longitude (or about 485 miles south of the mouth of the Mississippi River). Karen was moving to the north-northwest at 12 miles per hour. The central pressure of the storm was 29.65 inches of mercury (average sea level pressure is 29.92 inches of mercury).
The National Hurricane Center also posted a hurricane watch for coastal and immediate inland areas from Grand Isle, LA to Indian Pass, FL. They also posted a tropical storm watch for areas to the west of Grand Isle, LA to near Morgan City, LA. The tropical storm watch does include the metropolitan New Orleans area and Lake Ponchartrain.
A hurricane watch means that hurricane conditions (high winds and storm surge) are possible within the watch area. A hurricane watch is typically issued two full days (48 hours) before the first tropical storm force winds are expected in the area. A tropical storm watch is about the same, except that the threshold is only for tropical storm force winds.
Most computer models and the official National Hurricane Center forecast track bring Karen’s center northwestward toward southern Louisiana before curving the storm to the northeast for an early Sunday landfall near Mobile, AL. Karen is expected to approach or gain hurricane status by tomorrow morning and then remain at or near hurricane strength when she makes landfall. In addition to coastal storm surge flooding, heavy rains will be falling from Louisiana into southern Georgia before and following landfall. Heavy rains will likely fall along the entire Atlantic seaboard by early next week, as the storm becomes caught up in the middle latitude “westerlies” and accelerates northeastward.
Karen has the potential of becoming the strongest storm of an otherwise lackluster 2013 hurricane season. She also stands the best chance of bringing significant tropical weather to the U.S. A pretty good rule is that once a tropical storm or hurricane enters the Gulf of Mexico region, it almost certainly has to strike a landmass before its demise.
As of now (as noted earlier), Karen’s target area would seem to be the central to eastern Gulf Coast (eastern Louisiana to the Florida Panhandle). South Florida should be well-removed from Karen’s direct influence. However, with a very moist air mass in place, more heavy thunderstorms can be expected there for the next few days. As Karen moves away from south Florida, a trailing low-level convergence zone will likely be left behind. This should serve as a focus for further thunderstorm activity during the weekend.
© 2013 H. Michael Mogil
For the latest information on Karen (including safety actions), please check local National Weather Service, local media and other reliable sources.
Here are links to some key NWS forecast sites
Main NWS Page - http://weather.gov
National Hurricane Center – http://www.nhc.noaa.gov
South Florida NWS Sites –
Tampa Bay NWS
Key West NWS