Friday, August 24, 2012

Isaac Strengthening, Moving Northwest

Tropical Storm Isaac is now strengthening and appears to be in the process of beginning a northwest movement. Let's look at the past track of Isaac.

University of Wisconsin-Milwaukee
The observed track of Isaac shows a recent southern dip, followed by some regulation to the 16N longitude line. Recently, however, a sharp northwest turn was observed, bringing Isaac to about 16.5N. A northward turn is expected as Isaac strengthens. Strengthening of tropical systems commonly leads to the Coriolis effect taking over and turning storms to the north. The Coriolis effect will act as a tugboat, and veer storms to the right (north) in the northern hemisphere, and this could very well be happening now with Isaac.

The Advanced Dvorak Technique, which helps find the center of tropical systems, has pinpointed Isaac's location at about 16.5 N and 71.35 W in the Caribbean. Looking at the satellite image superimposed with the center of Isaac, we see that the center is dangerously exposed on the west side. When we have a center of circulation (COC) with such an exposed area, it can be very easy for the atmosphere to quickly weaken Isaac. If that should happen, I could see a southward wobble happen, and more model mayhem ensue.

The ADT also shows the strength of the system, based on satellite estimates and their own Cyclone Intensity scale, which ranges from 1 to 8 on this chart. Looking at recent observations, we see Isaac has endured some weakening in the past 24 hours. However, recent strengthening appears to be rebounding Isaac to a more stable point. This cannot be confirmed, however, until the center of circulation is re-covered.

Now... Model Mayhem Resumes!

Today's 12z European ECMWF model took a 967 millibar hurricane to the central Gulf Coast, keeping the consistency we look for and value so much in model forecasts. While the storm remains a while away, I am pondering this scenario. Isaac has already been shifting west and south and been strengthening and weakening so that a major move north has not been favorable. However, now, with the models recognizing the Gulf Coast threat, and a northwest movement seen above, this could be Isaac's time to shine, as far as moving towards the Gulf.

The GFS is much weaker, taking a 994 millibar tropical system to the Florida Panhandle. I do find this possible, but it is hard to go up against the consistency of the ECMWF. While this solution was shown in the 0z model suite last night, in which data from the Hurricane Hunters in Isaac was used, the ECMWF budged only a small amount east. Should Isaac take any wobble west, or even south, the ECMWF's solution would only become more and more likely.

The SREF is split, but many are projecting a tropical system to hit western Florida and the Panhandle, similar to the GFS. However, notice the major spread along the members. Just because you can make a big spread into a mean forecast does not mean it could be right. The wide variety of forecasts is very concerning to me, and I would like to not count in the SREF until its members can get into a good, solid solution.

Isaac is playing his tricks on us, and all you can do now is prepare. I advise (under my personal discretion, NOT the NHC's) that the Gulf Coast carefully monitor Isaac. The Florida Panhandle area, west to far eastern Louisiana should keep a close eye on Isaac, and consider making preparations for possible impact. We remain a time away, but the models seem to be coming together.


All advice and opinions shared on here are those of mine and are not those of the National Hurricane Center. In any case, always disregard my forecasts and advice in favor of the National Hurricane Center's. This is meant as an informative article and should not be used to make major decisions, such as evacuation.