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Tropical Storm Franklin Discussion Number   3
NWS National Hurricane Center Miami FL       AL072017
500 AM EDT Mon Aug 07 2017

Deep convection associated with Franklin has been steadily
increasing in both coverage and vertical depth since the previous
advisory.  Wind data from a late-arriving 0231Z ASCAT-A pass suggest
that Franklin might not have had a closed surface circulation at
that time. However, the new GOES-16 nighttime microphysics imagery
clearly shows low clouds moving from west to east on the south side
of the alleged center, which is suggestive of a closed low-level
circulation. The intensity has been nudged upward to 40 kt based on
sustained winds of 39 kt measured at 4-meters elevation from NOAA
buoy 42057 located about 110 nmi east of the center.

The initial motion estimate is 300/12 kt. The latest NHC model
guidance remains in excellent agreement that Franklin will continue
to move west-northwestward along the south side of a deep-layer
ridge during the next 48 hours or so, making landfall along the
east coast of the Yucatan peninsula in 18-24 hours. After the
cyclone crosses over Yucatan and moves into the Bay of Campeche by
Wednesday, a more westward motion is expected thereafter as the
ridge currently situated over northern Mexico and the southwestern
U.S. builds southward. The track model guidance is tightly clustered
around the previous forecast track, so the new forecast track is
just an extension of the previous one and lies down the middle of
the guidance envelope.

Upper-level outflow continues to expand in the western semicircle,
and a pronounced poleward outflow channel has developed in the
northern semicircle, which is being aided by a large upper-level low
located north of Puerto Rico. Although UW-CIMSS wind analyses
indicate that modest westerly mid-level shear is still affecting the
cyclone, that hindrance is forecast to abate in another 6 h or so.
Both the GFS and ECMWF models are forecasting the deep-layer and
mid-level shear to decrease to near zero in the 12-24 h period,
suggesting that Franklin could undergo a period of rapid
intensification right up until landfall occurs. Unfortunately, the
official intensity forecast does not directly reflect that possible
intensification trend due to the 24-h position being inland over
Yucatan with weakening occuring at that time due to land
interaction. Franklin is likely to reach a peak intensity of about
60 kt or so prior to landfall, and for that reason the government of
Mexico has issued a Hurricane Watch. The cyclone will weaken some as
it moves over the Yucatan, but re-strengthening is expected after
Franklin emerges over the very warm waters of the Bay of Campeche in
the 48-72 h period. The NHC intensity forecast remains close to the
higher SHIPS guidance at 24 hours, and is near the IVCN and HCCA
consensus models after that time.

FORECAST POSITIONS AND MAX WINDS

INIT  07/0900Z 17.1N  84.2W   40 KT  45 MPH
 12H  07/1800Z 18.0N  85.8W   50 KT  60 MPH
 24H  08/0600Z 19.0N  88.0W   55 KT  65 MPH...INLAND
 36H  08/1800Z 19.9N  90.2W   40 KT  45 MPH...INLAND
 48H  09/0600Z 20.4N  92.3W   45 KT  50 MPH...OVER WATER
 72H  10/0600Z 21.0N  96.4W   55 KT  65 MPH
 96H  11/0600Z 21.1N 100.5W   25 KT  30 MPH...INLAND
120H  12/0600Z...DISSIPATED

$$
Forecaster Stewart

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