Tropical Report

DEPRESSION MOVING FASTER TOWARD THE WEST-NORTHWEST OVER THE TROPICAL ATLANTIC…

Tropical Depression Four Discussion Number 2
NWS National Hurricane Center Miami FL AL042017
500 AM AST Thu Jul 06 2017

The cloud pattern of the tropical cyclone consists mainly of a
circularly shaped mass of deep convection that has persisted
overnight. Since there has been little overall change in the
satellite appearance of the system, the current intensity estimate
remains 25 kt, which is also in agreement with a Dvorak estimate
from SAB.

Dry and dusty air related to the Saharan Air Layer, to the east of
the tropical cyclone, is beginning to wrap around the northern part
of the depression’s circulation. Dynamical models indicate that
this air mass will be partially entrained into the system over the
next couple of days. This, combined with increasing vertical
shear, should prevent significant strengthening of the system.
Although the statistical-dynamical guidance, SHIPS and LGEM,
forecast some modest intensification of the tropical cyclone, these
models have been known to have a high bias at times. The GFS,
UKMET, and ECMWF global models all show the system quickly
degenerating to a wave. As a compromise between the global and the
statistical-dynamical guidance, the official forecast more or less
maintains the cyclone’s intensity for a couple of days followed by
weakening to a remnant low in 72 hours and dissipation after 96
hours.

The center is not very easy to locate, but based on continuity with
earlier data it is believed to be near the eastern edge of the
convective mass. There has apparently been some acceleration and
the motion is now estimated to be 290/15 kt. The flow on the
southern side of a subtropical ridge should continue to steer the
tropical cyclone, or its remnants, west-northwestward over the next
few days. The official track forecast follows a trajectory very
similar to the previous one, but is somewhat faster. This is close
to the latest model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT 06/0900Z 13.2N 40.0W 25 KT 30 MPH
12H 06/1800Z 14.0N 42.5W 30 KT 35 MPH
24H 07/0600Z 15.0N 46.2W 30 KT 35 MPH
36H 07/1800Z 16.3N 50.0W 30 KT 35 MPH
48H 08/0600Z 17.5N 53.5W 25 KT 30 MPH
72H 09/0600Z 20.5N 59.5W 25 KT 30 MPH…POST-TROP/REMNT LOW
96H 10/0600Z 23.0N 65.0W 20 KT 25 MPH…POST-TROP/REMNT LOW
120H 11/0600Z…DISSIPATED

$$
Forecaster Pasch

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
500 AM PDT Thu Jul 6 2017

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

1. Showers and thunderstorms continue to gradually become better
organized in association with a broad area of low pressure located
several hundred miles south of Manzanillo, Mexico. Environmental
conditions are expected to be favorable for additional development,
and this system is likely to become a tropical depression this
weekend while it moves generally westward to west-northwestward at
about 10 mph away from the coast of Mexico.
* Formation chance through 48 hours…medium…50 percent.
* Formation chance through 5 days…high…80 percent.

Forecaster Brennan

Weather In Cayman

Synopsis

Isolated showers are expected across the Cayman area as an upper level trough lingers over the Northwest Caribbean. Additionally a tropical wave over the western Caribbean may also lend support for showers and possible thunder over the next 24 hours as it moves towards Central America. Radar images show isolated showers in and around the Cayman area currently concentrated over the Sister Islands which are moving towards the west.