ZCZC MIATCDEP5 ALL
TTAA00 KNHC DDHHMM
Tropical Storm Irwin Discussion Number 24
NWS National Hurricane Center Miami FL EP102017
200 AM PDT Fri Jul 28 2017
Although conventional satellite imagery shows recent improvement in
the banding feature wrapping around the eastern half of the
cyclone, an ambiguity solution of a 0514 UTC ASCAT-B overpass
indicates that Irwin has weakened. Based on the scatterometer data
and a blend of the subjective Dvorak satellite estimates from TAFB
and SAB, the initial intensity is lowered to 45 kt for this
advisory. The CIMSS wind shear analysis and the SHIPS model both
indicate that moderate northeasterly shear, produced by an
anticyclone to the north, will be the primary inhibitor for any
significant strengthening prior to Irwin's demise in 4 days.
Little change in the cyclone's intensity is forecast before the
merging of Irwin with Tropical Storm Hilary occurs around the 96
hour period.
The initial motion estimate continues as a drift toward the
west, or 270/02 kt. The large-scale models indicate this slow
motion, or meander, continuing through the 36 hour period.
Afterward, Irwin is expected to accelerate northward around
the eastern peripheral flow of Hilary. The global and
regional models also generally agree with the merging of the two
tropical cyclones to occur in 4 days, or less. The official
forecast has been adjusted to the right of the previous track
forecast beyond 36 hours to align more closely to the TVCX and HCCA
consensus models.
FORECAST POSITIONS AND MAX WINDS
INIT 28/0900Z 14.9N 124.8W 45 KT 50 MPH
12H 28/1800Z 14.9N 124.9W 50 KT 60 MPH
24H 29/0600Z 15.0N 124.8W 50 KT 60 MPH
36H 29/1800Z 15.7N 124.5W 50 KT 60 MPH
48H 30/0600Z 17.4N 124.5W 45 KT 50 MPH
72H 31/0600Z 22.0N 126.3W 45 KT 50 MPH
96H 01/0600Z...DISSIPATED
$$
Forecaster Roberts
NNNN