Hurricane IRMA (Text)


Hurricane Irma Discussion Number   5...Corrected
NWS National Hurricane Center Miami FL       AL112017
1100 AM AST Thu Aug 31 2017

Satellite images indicate that Irma is rapidly intensifying.
Very deep convection has formed in the central dense overcast,
which is now displaying a small and clearing eye.  Dvorak estimates
were up to 77 kt at 1200 UTC, and since the cloud pattern continues
to quickly become more organized, the initial wind speed is set to
85 kt.

Irma has moved somewhat south of and slower than all of the model
guidance since yesterday.  Consequently, it stayed longer over the
warmer ocean temperatures away from the drier air to the north,
possibly allowing the rapid strengthening.  Irma should move over
cooler waters tomorrow with some increase in mid-level dry air, so
hopefully the hurricane's intensity will level off by then.  In a
few days, the hurricane will be moving over warmer waters with light
shear shown by all of the model guidance.  This should promote
further strengthening of Irma, and the NHC forecast shows an
extremely dangerous category 4 hurricane next week, similar to the
solutions provided by the HWRF and the ECMWF models. The intensity
forecast is raised considerably from the previous one due to initial
trends, and is on the high end of the guidance at long range.

The hurricane has turned west-northwestward at about 9 kt.  This
motion should continue for the next day or so before a ridge builds
over the central Atlantic Ocean.  This ridge should force Irma to
turn westward by the weekend, and west-southwestward early next
week. Guidance continues to trend southward, following the trend of
the ECMWF model starting yesterday.  Given the strength of the ridge
and depth of the tropical cyclone, there are no obvious reasons to
discount the anomalous west-southwestward motion seen in most of the
guidance. Little change is made to the track forecast in short
range, but the track is shifted southward and westward at long
range, though not as far southwest as the overnight ECMWF and ECMWF
ensemble models.


INIT  31/1500Z 16.9N  33.8W   85 KT 100 MPH
 12H  01/0000Z 17.5N  35.2W  100 KT 115 MPH
 24H  01/1200Z 18.0N  37.1W  105 KT 120 MPH
 36H  02/0000Z 18.2N  39.2W  105 KT 120 MPH
 48H  02/1200Z 18.1N  41.6W  105 KT 120 MPH
 72H  03/1200Z 17.0N  46.5W  110 KT 125 MPH
 96H  04/1200Z 16.0N  51.0W  110 KT 125 MPH
120H  05/1200Z 16.0N  55.5W  115 KT 130 MPH

Forecaster Blake


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Page last modified: Sunday, 31-Dec-2017 12:09:24 UTC