Aug 7 Monday 2017

Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Mon Aug 7 2017

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Tropical
Storm Franklin, located a couple of hundred miles east of Belize.

1. An elongated area of low pressure located about midway between the
Cabo Verde Islands and the Lesser Antilles is producing disorganized
shower and thunderstorm activity. Unfavorable environmental
conditions should limit development of this system during the next
few days, but conditions could become more conducive for some
increase in organization of this disturbance by the end of the week.
This system is expected to move generally west-northwestward across
the tropical Atlantic at about 15 mph during the next several days.
* Formation chance through 48 hours…low…near 0 percent.
* Formation chance through 5 days…low…20 percent.

Public Advisories on Franklin are issued under WMO header
WTNT32 KNHC and under AWIPS header MIATCPAT2.
Forecast/Advisories on Franklin are issued under WMO header
WTNT22 KNHC and under AWIPS header MIATCMAT2.

Forecaster Cangialosi

FRANKLIN GRADUALLY STRENGTHENING

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

 Tropical Weather Outlook
NWS National Hurricane Center Miami FL
500 AM PDT Mon Aug 7 2017

For the eastern North Pacific…east of 140 degrees west longitude:

1. An area of low pressure could form during the next day or so
several hundred miles south of the coast of Mexico. Development, if
any, of this system should be slow to occur while it moves
west-northwestward to northwestward.
* Formation chance through 48 hours…low…near 0 percent.
* Formation chance through 5 days…low…20 percent.

Forecaster Cangialosi