Hurricane Gustav Discussion

Hurricane Gustav is currently, per the NHC, a 980 mb hurricane with 75 mph winds to the northwest of Jamaica. The hurricane hunters have found winds up to 90 mph just 24 miles from the center of circulation, which tells me it is within the storms strengthening eyewall. I expect the NHC to up the winds at the 5 pm advisory. Even if they don't, however, this report helps to show that the storm is quickly strengthening and should be near category 2 status as it reaches the Cayman islands.




Gustav is situated in a very favorable environment for strengthening. The system is over the warmest sea surface temperature and tropical cyclone heat potential (TCHP) water in the entire tropical Atlantic. TCHP helps to indicate when rapid, or explosive, strengthening is possible. The waters around Gustav now, and until it reaches the center of the Gulf of Mexico, support rapid strengthening. Upper-level winds are also conducive, with little shear (near 5 knots) and an upper-level anti-cyclone developing over the system. The ridge to the northeast is steering Gustav towards the northwest.



The image above shows the GFS 700 mb forecast 60 hours into the future from the 12Z model run. The red area indicates the ridge that is currently situated through the United States and out into the Atlantic. The purple line indicates a trough that will be digging off of the eastern United States. All of the yellow circles show tropical waves or storms that are forecasted by the GFS model. Gustav is located in the Gulf of Mexico, Hanna off of the Florida coast, and then three more waves are shown in the Atlantic.



The ridge shown in this image is what should steer Gustav to the northwest until Monday. At that time, some of the models then forecast the ridge to build in stronger than the GFS forecast to the north of Gustav as it approaches Louisiana. This would cause Gustav to stall or push towards the west. Below are the models, with the European in red bold, UKMET in yellow bold (which should go a bit further west), and the HWRF in purple bold. As you can see, model trends are starting to indicate that a more western track is looking more likely. However, these models do not develop as deep a system as the GFS or GFDL, which forecast a more eastern landfall in central Louisiana towards New Orleans. A stronger system is much more likely to bust through a developing ridge than a weak system. Thus, the stronger Gustav becomes, the more likely it will make landfall in central Louisiana. However, all I said was more likely, not guaranteed. A stall could occur just as Gustav approaches Louisiana and the storm could move towards the LA/TX border.



Right now I am going to put my forecast track into the area just east (Creole, LA) of the LA/TX border as a Category 3 Hurricane. We should see rapid strengthening as Gustav moves over the Caribbean waters until it reaches Cuba, possibly reaching strong Cat 3 strength. Cuba should weaken the system a bit, and then weak shear should inhibit rapid strengthening over the Gulf of Mexico. The storm may increase back to a strong Cat 3 in the Gulf of Mexico before weakening slightly as it approaches the coast. A Cat 4 is possible either just before Cuba or after, but I do not expect it to hold that strength as it approaches the coast because TCHP waters are not quite as strong in the northern Gulf. We should also see a few eyewall replacement cycles along the way, which could cause strength fluctuations.