NHC Still Unsure of Isaac’s Location
As expected, Tropical Depression Ten became Tropical Storm Joyce this morning. The official forecast, including error, poses no threat to land, with the exception of Bermuda. Joyce could pass by the tiny island Mon or Tues as a tropical storm. At no point is Joyce expected to attain hurricane status. In fact, the closest it comes to doing so is at the end of the forecast period when the maximum sustained winds are forecast to increase to 60 mph – 14 mph shy of hurricane status. One interesting note about Joyce… it ties the 2nd-earliest formation of the 10th named tropical storm in a season. In 2005, Jose set the record when it was named on August 22nd. Joyce joins Jerry (1995) in 2nd place with a naming date of August 23rd. Of course, I’m not sure storms like Helene would’ve been named in the past, so this might skew the record book a little. (And records only go back so far.)
The NHC still isn’t sure of Isaac’s location. The 11AM EDT discussion notes the central circulation is not well-organized and there are “multiple low level vorticity centers rotating around a large area of light winds.” In an organized storm, there should be a core of strong winds around the center of the storm. To illustrate the disorganization of Isaac, here’s an infrared image of Isaac with the NHC-listed center:
You’ll note most of the convection (bright red) is south of the “center” of Isaac. The NHC admits in their discussion that the center of the storm according to aircraft data is north of the center suggested by satellite data. Why is this important? As I mentioned late last night, if we don’t know where Isaac’s center is, it is difficult to forecast where it will be in 1, 2, or 5 days. If, when established, Isaac’s center is 200 miles south of the current estimated location, that could significantly change where Isaac makes landfall in the Caribbean and US.
On the other hand, Isaac is an incredibly large storm right now. It is estimated at about 700 miles across or about the distance from Amarillo, TX to Brownsville, TX (almost the north-south extent of Texas). So, no matter where the center is, the effects will be felt far away from that point. Of course, the overall strength of the storm is dependent on the health of its’ center. The longer the center is over water, and the better defined it is, the stronger the storm will be. This is why we need to know where the center is very soon.
One final and curious note… the NHC’s intensity forecast calls for Isaac to become a category one hurricane in 36 hours. Their probability table for that forecast period states the best odds are Isaac is still a tropical storm at that time. Huh?