Saturday, August 25, 2012

Isaac Heads For The Gulf

Last night Isaac moved across Haiti dumping torrential rains on the poorest country in this hemisphere.  High winds and flooding rains pounded the country into the morning hours.  The center of Isaac moved across the southern mountains of Haiti, but then turned northward through the Windward Passage to reach the eastern tip of Cuba by midday.

Click on image to enlarge.  Image Credit: NOAA/NHC.

This is the latest plot of the path of Isaac with the associated wind field.  Notice how erratic the path has been since moving into the Caribbean.  This is due to the complex weather pattern over the region playing a tug-of-war with the storm and it is still happening.

Enhanced infrared satellite picture for 00:45z August 26, 2012.  Image Credit: NESDIS.

Tropical Storm Isaac did weaken some going over the mountains in Haiti.  However, the central circulation stayed intact and the storm jogged to the north before turning to the northwest upon reaching Cuba.  It has been moving along the north coast of Cuba during the afternoon and evening.  The interaction with land and kept the structure and little ragged with no strengthening.

However, Isaac avoided the mountains in eastern Cuba which could have greatly disrupted the circulation.  There are signs that the storm will strengthen as it moves away from Cuba.  In addition, the steering currents could turn it more to the west early in the morning pushing more toward Key West.  Rain bands are already moving into south Florida as seen Saturday evening from the Miami NWS radar.

NWS radar from Miami at 9:16 p.m. EDT August 25, 2012.  Image Credit: NWS

Computer simulations have flip-flopped during the past 24 hours.  This is true of the ECMWF, GFS, Canadian, and GFDL models.  Those forecasting a landfall in the lower Mississippi River Valley yesterday were pointing to the Florida panhandle today and vice versa. 

The ECMWF forecast for 12z on August 24 and 25, 2012.  Image Credit: WSI.
The GFS forecast for 12z August 24 and 18z August 25, 2012.  Image Credit: WSI.
What does this mean?

The simulations are having a hard time resolving the patterns that would ultimately steer the storm.  There is much uncertainty once the storm moves into the northern Gulf of Mexico.  Forecasters at the National Hurricane Center are having a hard time with the extended range forecast track and an even harder time with the forecast intensity.

The 5-day forecast for Isaac at 11 p.m. EDT August 26, 2012.  Image Credit: NOAA/NHC.

Do not be concerned much for the centerline track.  In this storm it has been of little use except to me.  The cone of uncertainty has been a better guide with the storm rarely being outside of it since forming.  This part of the forecast path has been good.

Bottom-line: Residents along the northern Gulf coast need to take this seriously.  There is a possibility for a major hurricane hitting the area by Tuesday.  Even if it doesn’t get that strong, there will be a considerable storm surge.  Heavy rain will be likely inland as the system slows down.  The path after that remains unclear.

I’ll have another look at the storm late Sunday.