
IWIC Hurricane Isabel Forecast 13, 11:30 AM EDT September 11 2003
Note: This forecast is unofficial, and is NOT from the National Hurricane Center. See our disclaimer.
Isabel is a dangerous hurricane to say the least. The Natioanl Hurricane Center has the storm at 130 knots as of 11am, though this could be too low given the intensity estimates of 140 knots from the Satellite Analysis Branch. If Isabel continues to organize, its maximum winds may increase more in the next advisory. At the moment, Isabel has a classic appearance. Outflow is outstanding in all quadrants, including the northern, which was hindered by the strong subtropical ridge yesterday. Isabel's eye has become perfectly circular, and the eyewall remains tight and well defined.
The environment ahead of Isabel looks ideal. Sea surface temperatures are in the mid 80s, plenty warm to sustain a major hurricane. CIMSS Saharan Air Layer analyses show very little Saharan dust in the vicinity of the system, which corresponds with moist air. Hurricane Heat Potential ahead of Isabel is also high. And to top it all off, wind shear profiles are expected to remain low, which will allow Isabel to maintain a symmetrical structure. Given the way the global models amplify the upper level anticyclone to the north of the storm over the next few days, Isabel's outflow should expand even more, mostly in the north and east. There are only two reasons that could be used to argue against strengthening. For one thing, the SHIPS model still rapidly weakens Isabel to a category 1 system in 5 days. Also, a hurricane can only intensify so much before leveling off due to complex atmospheric dynamics; rarely do Atlantic hurricanes strengthen more than Isabel is now. However, since Isabel still appears to be in an intensification mode, I will forecast another 5 knot increase within the next 12 hours, and then show just very slight weakening beyond that time. In all honesty, I am not sure why the SHIPS shows so much weakening, but since it did the same with Fabian, and is not the most reliable intensity model anyways, I will ignore it for right now. Keep in mind that fluctuations usually occur in strong hurricanes such as Isabel because of eyewall replacement cycles.
At the moment, Isabel is located to the south of a very strong low to mid level ridge. This ridge is steering the storm westward, as seen in the latest satellite loops. Isabel has and will continue to wobble to the north here and there, but the overall motion is near due west. Most of the models are in agreement on this motion to continue through the next 2 days as the ridge changes little in position and intensity. Beyond that timeframe things start to change. Currently there is a frontal low, the remnants of Tropical Storm Henri, situated off the Carolina coast. Almost all of the models show some slight intensification as it slowly moves to the north. Given the recent increase in convection and organization, that seems liable. Provided the strengthening occurs, the effect will be a erosion of the western prehiphery of the ridge. In turn, Isabel will be steered more to the west-northwest after the 2 day timeframe. This turn is depicted in the most recent run of the tropical models, which made the dramatic shift further to the north last night. To put things a little simpler, I am soled on a continued westward motion through the next 2 days followed by a track more towards the west-northwest during the rest of the 5-day forecast period.
The situation becomes a little more complicated in the longer run. At the very end of the period, the setup will probably look something like this: Isabel a good distance to the northeast of the Bahamas, a somewhat eroded ridge to the north, and a strong mid latitude trough approaching eastern portion of the United States. While the remnants of Henri will weaken the ridge some, at the moment I do not see it weakening it enough to steer Isabel off to the north for good. In fact, there is a good chance the ridge will build back immediately, as the AVN and NOGAPS may be suggesting. This would keep Isabel on a west-northwest track or even possibly cause it to bend a little more to the west. The key feature, however, will be the mid latitude trough. The models are starting to trend more towards a stronger trough, making it likely to pull Isabel northward whenever it gets close enough to do so. But that is the big question right now; when will it pull Isabel, and will it be able to save the east coast? Unfortunately, this question remains unanswered as it is a long range issue. Based on the model runs, the slight pull from Henri, and the magitude of the trough, it appears that Florida is not in as high of a risk as it was yesterday. Does this mean that Florida is completely out of the woods? Of course not. Since any possible east coast landfall would occur in approximately a week or so, it is too soon to say who is safe and who is not. For that matter, it is too soon to even say whether Isabel will hit or not. What I do know is that Isabel is a powerful storm, and by all means anybody living from southern Florida to the mid Atlantic coast, and the Bahamas, should closely monitor its progress.
Forecast Intensity:
00 hours: 130 knots
12 hours: 135 knots
24 hours: 135 knots
36 hours: 130 knots
48 hours: 130 knots
72 hours: 125 knots
96 hours: 125 knots
120 hours: 125 knots
Forecast Track: