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October 2012

Sandy to Hit Jamaica, Cuba, Bahamas while Strengthening, then Possibly Become Hybrid E. Coast Storm

   Posted by Levi at 4:16pm on October 23, 2012

Tropical Storm Sandy has formed in the western Caribbean, and continues to gradually deepen. Thunderstorm coverage and density has increased during the last couple of days, and a well-defined center has now formed. The western side of the storm remains void of thunderstorms for now, but that will change as the storm moves northward. Sandy’s present movement is nearly stationary, but she will begin to move northward today in response to a tightening pressure gradient over the Bahamas. This will bring Sandy over Jamaica in 24-36 hours. Steady intensification is expected during this time, and Sandy is expected to be a strong tropical storm and possibly even a minimal hurricane upon landfall in Jamaica. Sandy will then pass over eastern Cuba and into the Bahamas, where the upper-level environment will consist of some southerly wind shear, but also strong divergence aloft east of a negatively-tilted upper trough axis over the Gulf of Mexico, which should allow Sandy to wrap moisture around her center and continue to deepen into a Cat 1 hurricane, possibly a Cat 2 if she tightens her core quickly.

A late season hurricane should be fairly routine for this region to deal with, but the forecast becomes possibly more dangerous in the long term, as Sandy may get captured by a mid-latitude trough and bomb out into a strong hybrid nor’easter in 6-8 days. The model solutions provided by the ECMWF and CMC depict what would be one of the strongest Autumn storms the east coast has ever seen. The video discusses this aspect of the forecast in detail. Right now the GFS is the last model that allows Sandy to escape the trough and move northeastward out to sea. Due to the developmental structure that Sandy is likely to have in the Bahamas which is favorable for phasing, the interaction with the upper trough to her west, and the blocking over maritime Canada, a more westward path than the GFS seems more likely to me at this time. The forecast track is a blend of the ECMWF and UKMET ensembles. The forecast cone indicates the large amount of uncertainty in the 4-6 day forecast, as it is not out of the question that Sandy still tries to escape to the east. Much will depend on the exact timing of the incoming mid-latitude trough, something the models have been varying greatly on, and the convective structure of Sandy in the Bahamas, which can influence her track tendencies. Jamaica, Cuba, the Cayman Islands, Hispaniola, and the Bahamas should all expect direct impacts from Sandy. Florida will likely get some blustery weather, and New England should keep a close eye on this situation, for a storm of the magnitude that is possible in this kind of a situation would be unprecedented, and the potential impacts could be severe.

We shall see what happens!