Baltimore, MD - Tropical storm Isaac continues to be forecasting challenge not in the short term but in the medium range forecast.
The models have gone from suggesting a land falling hurricane on the east coast earlier this week to a Tampa Hurricane threat. The new overnight forecast models have now shifted further north however; our trusted friend the European model continues to stay the course with a southern solution.
Two of our 4 global models I look at actually have a MISS on south Florida with Isaac cutting just east of Miami and making a landfall from Georgia to North Carolina! Sounds Crazy right?! Maybe not!
Here is the official track from the National Hurricane Center as of 2AM
GFS : Isaac tracks just west of the mountainous terrain over Hispaniola. The trend has been north on this model. Just 12 hours ago it suggested a landfall over Tampa now it has shifted to a landfall over the Keys / Miami. Confidence weight: 45%
EURO : This model for days has suggested a western moving Isaac until it reaches Cuba. At this time it moves WNW and into the Gulf of Mexico. The intensity remains at and around a minimal to moderate Tropical Storm gaining Hurricane status by late weekend.
Confidence weight: 30%
CMC : The Canadian model continues to indicate a WEAK subtropical ridge which spells out a more northern solution. One has to look at this model and give it weight considering the GFS has trended north opposed to south to come in line with the EUROPEAN model. The Canadian has not had the best track record with tropical systems however, has had a few hits. It correctly predicted Irene in the 11 th hour siding with the European.
Confidence weight: 15%
Navy NoGAPS : Not my favorite model. It suggests a similar scenario to the CMC however, has never been a great tropical model. This model is notorious for erratic shifts in tropical model tracks. In the last 24 hour it has corrected the track of Isaac some 100 miles to the west however, the 00z and 12z Aug 21/22 st runs have settled on a track solution just east of Florida going into SC/NC
Confidence weight: 10%
LOOKING AHEAD :
The ultimate short range path will be decided in just a couple of days which will come down to the intensity of Isaac. If he remains a weak system it will stay to the south of the islands and the European track solution will verify. However, a stronger system will curve more north and the effects of TWO main weather variables will dictate its move beyond the next 5 days.
A trough of low pressure is expected to move through the norther tier of the US by the weekend. Troughs this time of the year tend to be a little stronger then the models project them to be. If the timing and intensity of this trough matches to the precise time Isaac is north of the islands (trough being stronger vs weaker) then Isaac will move north and the CMC and NOGAPS solutions will verify. This means heavy rain, high winds, coastal concerns, and tornados will be a threat from Florida to Virginia (maybe further north). I outlined the % likelihood above with the track solution coming to fruition.
The subtropical ridge (HIGH PRESSURE SYSTEM) parked north east of Isaac will be another player in the long range. A stronger high will suppress Isaac further south ALA the European track solution. If that's the case then we have a Gulf coast CANE threat by next week. However, a weaker solution to the high could allow a more northerly component to Isaac bringing a solution similar to what the GFS suggests with shades of a easterly component (meaning the track could be right off the east coast of Florida) !
The bottom line is the intensity of three things must be figured out by the models. First, Isaac (including the intensity gained or loss once it interacts with Hispaniola and waters near the island.), Second, the subtropical ridge, and Third the trough expected to enter the USA by this weekend.
More details to come !