re: Hurricane Irma - Spinning Down

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Hurricane Irma Discussion Number 40
NWS National Hurricane Center Miami FL AL112017
1100 PM EDT Fri Sep 08 2017

An Air Force Hurricane Hunter flight has found that Irma has
re-intensified to category 5 strength. The plane measured a
maximum flight-level wind of 154 kt and SFMR winds of 140-145 kt in
the northwestern eyewall, so the initial intensity is raised to 140
kt. The hurricane is producing very deep convection in all
quadrants around the eye, which the Air Force flight measured to be
35 n mi wide.

Apparently the ridge to the north of Irma has been stronger than
expected, and the initial motion remains westward, or 280/11 kt.
The track guidance continues to insist on Irma turning
west-northwestward soon, moving along the Cuban Keys adjacent to
the north coast of Cuba during the next 24 hours. After that time,
Irma is expected to turn sharply north-northwestward and accelerate
after 48 hours, moving parallel to the west coast of Florida and
then into Georgia. Mainly because Irma's eye has not deviated from
its westward motion, the new NHC forecast track has again shifted
slightly westward. Because of the hurricane's angle of approach to
the west coast of Florida, it is extremely difficult to pinpoint
exactly where the center might move onshore.

If the eye continues to move over the Cuban Keys and does not move
inland over the main island of Cuba, then Irma would likely not
lose much intensity during the next day or so. As we've stated
many times, fluctuations in intensity are likely during the next 36
hours due to possible and unpredictable eyewall replacement cycles.
After 36 hours, there are some indications that vertical shear may
increase over the hurricane, and a little more weakening is
anticipated at that time. Because of the concerns in the track
forecast noted above, Irma would be able to maintain a strong
intensity for a longer period of time if the center stays off the
west Florida coast. Regardless, Irma is still expected to be a
dangerous hurricane as it approaches the Florida Keys and the west
coast of Florida through 48 hours.

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