Tropical Storm Isaac–The BIG Tease

Storm Continues To Flirt With Intensification, But Still Shy Of Being A Hurricane

Despite all of the fanfare and the numerous opportunities, Tropical Storm Isaac remains just that…a tropical storm. The system has undergone some slight strengthening since this time last night. Minimum central pressure has fallen about 14 millibars including two with the last advisory at 11:00 PM EDT, or 10:00 PM CDT on Monday night while maximum sustained winds have crept up to just below minimal hurricane force at 70 miles per hour.

However, Isaac is still not quite there. The overall circulation remains lopsided. Now, the bulk of the convection is in the southern half of the storm. Last night, it was in the northern and eastern side. Isaac is still battling a lot of dry air. Quite similar to what happened with Hurricane Irene last year after it pass through the Bahamas, and then showed brief signs of strengthening. As with Irene, the dry air could be the savior here for the Big Easy and the rest of the Northern Gulf Coast.

Now located some 200 miles or so from the mouth of the Mississippi River, and slowing down to only move at a forward speed of just 10 miles per hour, Isaac still has a good deal of time to strengthen, especially over the very warm waters of the Gulf. The NHC is calling for the storm to intensify to a strong Category One Hurricane on the Saffir-Simpson Scale with 90 mile per hour winds. There could be an outside chance of it reaching Cat Two, but that opportunity is fading.

Isaac is still a very vast storm system with tropical storm force winds extending some 200 plus miles from the center of circulation. Feeder bands from the storm have been even pushing rain ashore in parts of South Carolina and Georgia up to 750 miles away from Isaac’s center. Pressure is also very low for even a strong tropical storm like Isaac at 979 millibars. Pressure like that is often seen in Category Two Hurricanes. There are other indicators that point to the storm getting better organized. Hurricane Hunter aircraft is indicating that the mid-level low is now moving over the top of the surface low making the storm more vertically stacked, which is a sign of strengthening.

Thunderstorm activity is again developing around the center of circulation, but we’ve seen this before with Isaac. All through its lifetime, it has been teasing us with these signs of strengthening, and then leveling off, or even weakening. The storm appears to be moving in a westerly direction, but forecast models and forecast analysis indicates that a trough over the Midwestern United States should push eastward, and cause the ridge off the East Coast of the United States to retreat, which will create a weakness over the Northern Gulf states that Isaac will exploit.