Oct 4, 2013

Another Update on Karen

Karen continues as a rather poorly organized tropical storm, battling the nemesis of many a tropical cyclone: strong wind shear and dry air. As shown below on the lower left image strong westerly shear of 20-25 knots continues across the cyclone and this is displacing the convection off to the east of the lower level surface circulation. The dry air is evident on the the water vapor satellite imagery (shown to the lower right) and is highlighted in the brown color. This dry air is drawn into the storm's circulation.

Based on the latest recon data from hurricane hunter aircraft, the storm has weakened a bit; the central pressure has risen (up to 1003 millibars) and the winds have decreased to 50 mph. The system is also wobbling on NW-NNW heading of around 10 knots or so. The dilemma facing the forecast is two-fold: 1) the future track and where it eventually makes landfall and 2) its intensity changes - will it continue to weaken, hold its own or perhaps intensify slightly before land fall.

A weaker tropical cyclone, being not well developed tends to be steered by winds in the lower levels of the atmosphere. Two of the four primary global models that are used in tropical cyclone forecasting - the UK and EC models are more west with the track of Karen. The other two models the GGEM (from Canada) and the GFS (the U.S. model) are more east with the GFS the farthest east and also indicating both a stronger and better organized tropical system. Based on the past motion of the storm the EC and UK appear to be doing better on the track and also the strength ( indicating a weaker cyclone). Because of this the tropical storm warning has been extended westward along the coast of Louisiana. This warning is now in effect from Grand Isle to Morgan City. The hurricane Watch remains posted for the moment from Grand Isle Louisiana to west of Destin, Florida but MAY BE discontinued later today or changed to a tropical storm watch or warning later today. So ultimately where Karen makes landfall is still up in the air at this point in time.

The system will ultimately make landfall over the weekend, over southeast Louisiana late Saturday then turning toward the northeast during Sunday as a non-tropical trough of low pressure approaches from the west.  The more west track would now favors the remnants of Karen being absorbed by the trough's cold front on Monday over the western part of South Carolina with the remnants of Karen moving northeast along the cold front as the front itself slides east to the East Coast by Tuesday.

Right now it looks like the heaviest rains of the combined cold front plus Karen's remnants will extend from the Southeast States to the eastern half of Virginia  and the Chesapeake Bay and the Delmarva Peninsula during the Monday-Tuesday time frame. While only moderate rains are forecast for now across Pennsylvania to NY State and western New England (most of this falling late Monday night into Tuesday).

More updates to follow

Oct 3, 2013

Some Quick thoughts on Tropical Storm Karen

The 11th named tropical cyclone of the season has formed over the Southeastern Gulf of Mexico - Karen. It was located about 500 miles south of the Mouth of the Mississippi River with maximum winds of 60 mph, and moving toward the northwest at around 13 mph. Karen is forecast to turn north and slow down over the next 24-36 hours as well as strengthen to a hurricane during this time. By Sunday, forecast environmental conditions will become unfavorable as the storm nears the U.S. Gulf Coast and some weakening is expected. Nonetheless Tropical Storm and Hurricane Watches have been posted for the Northern Gulf Coast.

(Current position and wind radii + Watches)
The forecast track of Karen (map below) has it nearing the Central Gulf Coast by early Saturday morning, October 5th and then making landfall over the western Florida Panhandle by Saturday afternoon.
(Official NHC forecast track for Karen)

Forecast model consensus is in fairly good agreement on the expected track of Karen. After landfall the system will weaken into a tropical depression and move a bit more quickly toward the northeast during Sunday through Monday of next week as it begins to interact with an expansive non-tropical area of low pressure that will extend from the Great Lakes to the Lower Mississippi Valley states. The remnants of Karen and this low pressure area will continue east and reach the East Coast of the U.S. by late Monday-Tuesday of next week. 

The early track guidance (map below and to the right) is clustering slightly to the east of the official NHC track forecast but again the early guidance is clustered around a landfall over the Florida Panhandle. 
(Early tropical cyclone guidance)

By early next week the interaction of Karen's remnants with the non-tropical low pressure area approaching from the west, could lead to widespread and potentially/possibly heavy rainfall for the Eastern States, especially from the Western Carolinas northward through the Mid-Atlantic States, Pennsylvania, interior central and eastern NY State and Western New England. I'll have more on this rain fall threat later today but I can say that there are numerous "signals" in the forecast data that favor some heavy rain for interior Eastern NY State and Western New England during early next week. How heavy? That is a question yet to be answered; then again we have been VERY dry as of late so any rain fall may actually be beneficial as long as its not EXCESSIVE.