Aug 8 Tuesday 2017

Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Tue Aug 8 2017

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

The National Hurricane Center is issuing advisories on Tropical
Storm Franklin, located inland over the Yucatan peninsula.

1. A trough of low pressure located about 800 miles east of the Lesser
Antilles continues to produce an area of disorganized showers and
thunderstorms. Development of this system is not expected during the
next few days due to unfavorable environmental conditions. However,
some development of this system is possible this weekend while the
system moves generally west-northwestward at about 15 mph over the
western Atlantic.
* Formation chance through 48 hours…low…near 0 percent.
* Formation chance through 5 days…low…30 percent.

Forecaster Cangialosi

FRANKLIN MOVING OVER THE YUCATAN PENINSULA

Tropical Storm Franklin Discussion Number 7
NWS National Hurricane Center Miami FL AL072017
400 AM CDT Tue Aug 08 2017

The Belize Doppler weather radar indicates that Franklin’s
inner-core circulation has tightened up considerably since the
previous advisory, likely due to frictional convergence, and that a
10-15-nmi-diameter closed eye has developed. Radar reflectivity
values have been steadily increasing in the eyewall, and this
development trend is supported by infrared satellite imagery, which
shows deep convection with cloud tops of -75C to -80C now completely
covering the radar eye. The initial intensity is lowered to 45 kt
for this advisory based on a typical decay rate for landfalling
tropical cyclones.

The initial motion estimate is 290/12 kt, based primarily on radar
data. A deep-layer subtropical ridge that currently extends across
the northern and central Gulf of Mexico is expected to remain intact
through the forecast period, building slightly southward by 48 h and
beyond. This entrenched steering pattern is expected to keep
Franklin moving west-northwestward across the Yucatan peninsula the
next 24 h or so, followed by westward motion across the Bay of
Campeche until landfall occurs in 48-60 h. NHC model guidance
remains in good agreement on this track scenario, and only a slight
nudge to the south of the previous forecast track was required due
to the more southward initial position of Franklin.

Additional weakening is expected while Franklin moves across the
Yucatan peninsula during the next 15 h or so. The recent inner-core
structural improvements are expected to remain in place by the time
the cyclone emerges over the warm waters of the Bay of Campeche.
That, combined with low vertical shear values and a well-established
outflow pattern, will allow for restrengthening to occur by
Wednesday, possibly resulting in Franklin achieving hurricane status
around 36-42 h. However, the GFS and ECMWF models are still
forecasting significant northerly vertical shear near 20 kt to
develop by 36 h and beyond, which could cap the intensification
process or possibly even induce some weakening since mid-level dry
air entrainment will accompany the northerly shear. However, since
Franklin is expected to be near hurricane strength at landfall, a
Hurricane Watch for mainland Mexico is warranted. The new NHC
intensity forecast is similar to the previous advisory, and closely
follows a blend of the HCCA and IVCN intensity consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT 08/0900Z 19.3N 88.5W 45 KT 50 MPH…INLAND
12H 08/1800Z 19.7N 90.2W 35 KT 40 MPH…INLAND
24H 09/0600Z 20.1N 92.4W 50 KT 60 MPH…OVER WATER
36H 09/1800Z 20.3N 94.4W 60 KT 70 MPH
48H 10/0600Z 20.2N 96.6W 60 KT 70 MPH
72H 11/0600Z 19.7N 101.8W 20 KT 25 MPH…INLAND
96H 12/0600Z…DISSIPATED

$$
Forecaster Stewart

 Tropical Weather Outlook
NWS National Hurricane Center Miami FL
500 AM PDT Tue Aug 8 2017

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

1. An area of low pressure could form a couple of hundred miles south
of the southern tip of the Baja California peninsula late this week
in association with the remnants of Atlantic Tropical Storm Franklin
after it moves across southern Mexico. Environmental conditions
could be conducive for some re-development of the system while it
moves toward the west-northwest or northwest near 10 mph.
* Formation chance through 48 hours…low…near 0 percent.
* Formation chance through 5 days…low…20 percent.

Forecaster Cangialosi