Jul 19 Wednesday 2017

Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Wed Jul 19 2017

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

1. An elongated low pressure area located about midway between the
Cabo Verde Islands and the Lesser Antilles is producing a large
area of disorganized showers and thunderstorms. Some gradual
development of this system is possible during the next day or
two while it moves toward the west-northwest or northwest at
10 to 15 mph. After that time, environmental conditions are
forecast to become unfavorable for development.
* Formation chance through 48 hours…low…30 percent.
* Formation chance through 5 days…low…30 percent.

Forecaster Brown

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
500 AM PDT Wed Jul 19 2017

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

The National Hurricane Center is issuing advisories on Hurricane
Fernanda located well to the east of Hilo, Hawaii, on Tropical
Storm Greg located several hundred miles southwest of Manzanillo,
Mexico, and on Tropical Depression Eight-E located several hundred
miles southwest of the southern tip of the Baja California
peninsula.

1. A tropical wave located south of the Gulf of Tehuantepec is
producing disorganized cloudiness and thunderstorms. Environmental
conditions are conducive for gradual development of this system
during the next several days and a tropical depression could form
well southwest of the southwestern coast of Mexico over the
weekend.
* Formation chance through 48 hours…low…near 10 percent.
* Formation chance through 5 days…medium…60 percent.

2. Another area of low pressure is forecast to form south of the
southeastern coast of Mexico over the weekend. Some gradual
development of this system is possible early next week.
* Formation chance through 48 hours…low…near 0 percent.
* Formation chance through 5 days…low…20 percent.

Public Advisories on Tropical Depression Eight-E are issued under
WMO header WTPZ33 KNHC and under AWIPS header MIATCPEP3.
Forecast/Advisories on Tropical Depression Eight-E are issued under
WMO header WTPZ23 KNHC and under AWIPS header MIATCMEP3.

Forecaster Brown

Tropical Storm Greg Discussion Number 8
NWS National Hurricane Center Miami FL EP072017
300 AM MDT Wed Jul 19 2017

The increased convective organization of Greg proved to be
short-lived. Although the SHIPS-analyzed shear remains low, the
cloud pattern now resembles that of a sheared tropical cyclone. A
0458 UTC ASCAT-B overpass caught the eastern half of the
circulation, showing no winds above 30 kt, while Dvorak-based
estimates of the current intensity range from 45 to 57 kt. The
initial intensity has only been lowered to 40 kt since the ASCAT
pass missed the western half of the circulation, but this could be
generous.

Based on the aforementioned ASCAT pass, the analyzed center of the
tropical storm has been shifted farther south, and the overall
track forecast nudged southward accordingly. While the reasoning
behind the forecast is unchanged, the model spread is still fairly
high, and run-to-run consistency is low. For instance, the 120-h
forecast points from the 18Z and 00Z GFS model differ by nearly 300
nmi. The CMC, ECMWF, GFS, and UKMET global models still show Greg
and TD Eight-E interacting to various degrees, with each cyclone
beginning to affect the others track in about 36 hours. This
interaction should ultimately cause Greg to accelerate toward the
west-northwest. After about 72 hours it is still assumed that Greg
will be the dominant cyclone, so only a slight turn back toward the
west-southwest is forecast. If TD Eight-E instead becomes dominant,
then a more pronounced southern turn would be expected.

Although the initial intensity is a little lower than the previous
advisory, most of the guidance still suggests that Greg will
gradually strengthen within a warm-SST, high-moisture, low-shear
environment for the next 24-36 hours. Thus little change has been
made to the intensity forecast, which remains near the IVCN and HCCA
consensus aids. If TD Eight-E becomes the dominant cyclone, an
alternate scenario is that Greg will dissipate much sooner than
currently forecast.

FORECAST POSITIONS AND MAX WINDS

INIT 19/0900Z 14.3N 111.0W 40 KT 45 MPH
12H 19/1800Z 14.4N 112.4W 45 KT 50 MPH
24H 20/0600Z 14.8N 114.3W 50 KT 60 MPH
36H 20/1800Z 15.4N 116.4W 55 KT 65 MPH
48H 21/0600Z 16.0N 118.9W 55 KT 65 MPH
72H 22/0600Z 16.9N 124.0W 40 KT 45 MPH
96H 23/0600Z 15.8N 129.1W 30 KT 35 MPH
120H 24/0600Z 15.0N 134.0W 25 KT 30 MPH…POST-TROP/REMNT LOW

$$
Forecaster Zelinsky

Tropical Depression Eight-E Discussion Number 4
NWS National Hurricane Center Miami FL EP082017
200 AM PDT Wed Jul 19 2017

The overall convective pattern of the depression has changed little
since the previous advisory and remains ragged looking. Cloud tops
colder than -70C have persisted near and to the south of the
low-level center, yielding satellite estimates of T2.5/35 kt from
SAB and UW-CIMSS ADT. However, the intensity will remain at 30 kt
for this advisory since a 0500Z ASCAT-B overpass indicated a few
wind vectors of 27-28 kt in the southwestern quadrant.

The initial motion estimate is 20/05 kt. There is no significant
change to the previous track forecast or reasoning. The global and
regional models are in decent agreement on the depression engaging
in some weak binary interaction with the larger circulation of
Tropical Storm Greg as the latter cyclone passes about 200 nmi to
the north over the next few days. The new forecast track is similar
to the previous advisory track and lies near the TVCN consensus
model.

The upper-level westerly outflow on the east of Hurricane Fernanda
is expected to keep the depression in a moderate to strong vertical
wind shear regime for the next couple of days. After that,
northerly outflow from Greg should act to maintain unfavorable
shear conditions across the depression, preventing any significant
strengthening until the system dissipates by 96 hours. The new
intensity forecast is identical to the previous advisory and
follows the consensus model IVCN.

FORECAST POSITIONS AND MAX WINDS

INIT 19/0900Z 14.6N 120.8W 30 KT 35 MPH
12H 19/1800Z 14.3N 121.4W 30 KT 35 MPH
24H 20/0600Z 13.8N 122.1W 25 KT 30 MPH
36H 20/1800Z 13.3N 122.7W 25 KT 30 MPH
48H 21/0600Z 12.9N 123.1W 25 KT 30 MPH
72H 22/0600Z 13.2N 124.1W 25 KT 30 MPH
96H 23/0600Z…DISSIPATED

$$
Forecaster Stewart