Sea surface temperatures near Ernesto in the northeastern Caribbean
Sea are very warm--on the order of 29-30 degrees Celsius--and
vertical shear in the atmosphere is relatively light. Combined
with the thought that Ernesto is developing an inner core, these
ingredients favor quick strengthening over the next day or so.
SHIPS and the HFIP Corrected Consensus models indicate that Ernesto
could be near or at hurricane strength in about 24 hours, and
several of the Rapid Intensification (RI) indices are notably high.
As a result, the updated NHC intensity forecast is more aggressive
than the previous forecast, and brings Ernesto to hurricane
strength by 24 hours when the center is north of Puerto Rico.
Because there is some risk of the storm becoming a hurricane before
that time, a Hurricane Watch has been issued for the Virgin
Islands, Culebra, and Vieques. After moving north of Puerto Rico,
additional strengthening is likely, and the NHC forecast is near the
high end of the guidance. Ernesto is also likely to grow in size
while over the western Atlantic, and that is reflected in the
official forecast.
Also note that despite the hurricane models showing MH intensity for the peak, the statistical guidance is still within the Cat 2 range, and thus NHC's 95 kt peak is near the "high end of the guidance".
