Aug 13 Sunday 2017

Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
200 AM EDT Sun Aug 13 2017

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

The National Hurricane Center is issuing advisories on newly formed
Tropical Depression Eight, located about 260 miles east of the
southeastern Bahamas.

1. A tropical wave that has just emerged off the west coast of Africa
is forecast to move westward over the next couple of days and merge
with a broad area of low pressure located southwest of the Cabo
Verde Islands. Thereafter, environmental conditions are expected to
be conducive for gradual development of the system while it moves
westward to west-northwestward at 10 to 15 mph over the open
tropical Atlantic Ocean.
* Formation chance through 48 hours…low…near 0 percent.
* Formation chance through 5 days…low…20 percent.

Public Advisories on Tropical Depression Eight are issued under WMO
header WTNT33 KNHC and under AWIPS header MIATCPAT3.
Forecast/Advisories on Tropical Depression Eight are issued under
WMO header WTNT23 KNHC and under AWIPS header MIATCMAT3.

Forecaster Stewart

Tropical Depression Eight Discussion Number 2
NWS National Hurricane Center Miami FL AL082017
500 AM EDT Sun Aug 13 2017

Satellite-derived winds from ASCAT passes at 0122Z and 0208Z
indicated that the tropical depression had a closed surface
circulation with peak winds of 33 kt in the southeastern quadrant.
However, those peak winds were occurring in the same area of the
circulation where NOAA Buoy 41046, which several hours ago measured
a sustained wind of 35 kt and a peak gust to 43 kt, due to what
appears to have been cold, downdraft-driven wind gusts based on a
sharp decrease in the temperature and dew point values. As a result,
the intensity will be held at 30 kt for this advisory, in line with
a consensus 30-kt estimate from TAFB, SAB, and UW-CIMSS ADT.

The initial motion estimate is 335/12 kt. The depression is forecast
to move north-northwestward to northward for the next 36 h around
the western portion a deep-layer subtropical ridge that is oriented
east-west along 30-32N latitude. By 48 h and beyond, a vigorous
shortwave trough currently located over the northern Plains is
expected to dig east-southeastward and weaken the ridge along the
east coast of the United States from the Carolinas northward to New
England. The increasing southwesterly flow ahead of the trough is
forecast to accelerate the cyclone northeastward, on an optimal
track about midway from the U.S. and Bermuda and keeping it away
from those two land masses. The new NHC tack forecast is similar
to the previous advisory, and lies close to a blend of the HCCA and
TVCN consensus track models.

The depression is expected to remain in a relatively low vertical
wind shear environment for the next 24-36 hours, but also within a
fairly dry mid-level moisture environment for the duration of the
forecast. As a result, only modest strengthening is expected during
the next couple of days. By 48 h and beyond, southwesterly vertical
wind shear is expected to steadily increase to more than 20 kt ahead
of the aforementioned shortwave trough, reaching 40-50 kt by 96-120
h, which should act to cap any additional intensification. Owing to
the strong shear, the cyclone is forecast to become extratropical by
days 4 and 5. The official intensity forecast is similar to the
previous advisory, and lies close to the consensus models IVCN and
ICON. The intensity forecast at 96 and 120 h reflects guidance
provided by the NOAA Ocean Prediction Center.

FORECAST POSITIONS AND MAX WINDS

INIT 13/0900Z 26.5N 70.9W 30 KT 35 MPH
12H 13/1800Z 28.1N 71.7W 35 KT 40 MPH
24H 14/0600Z 29.9N 72.2W 40 KT 45 MPH
36H 14/1800Z 31.5N 72.0W 45 KT 50 MPH
48H 15/0600Z 33.4N 71.0W 50 KT 60 MPH
72H 16/0600Z 37.7N 64.1W 50 KT 60 MPH
96H 17/0600Z 42.4N 50.8W 45 KT 50 MPH…POST-TROP/EXTRATROP
120H 18/0600Z 46.3N 36.5W 45 KT 50 MPH…POST-TROP/EXTRATROP

$$
Forecaster Stewart

 Tropical Weather Outlook
NWS National Hurricane Center Miami FL
500 AM PDT Sun Aug 13 2017

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

The National Hurricane Center is issuing advisories on Tropical
Depression Jova, located a few hundred miles west-northwest of
Socorro Island.

1. A surface trough located a few hundred miles south of Acapulco,
Mexico, is producing disorganized showers and thunderstorms.
Environmental conditions are forecast to gradually become more
conducive for development in a few days, and a tropical depression
could form late this week while the system moves westward to
west-northwestward at around 10 mph.
* Formation chance through 48 hours…low…10 percent.
* Formation chance through 5 days…medium…60 percent.

2. An area of low pressure is expected to form several hundred
miles southwest of Manzanillo, Mexico, in a few days. Although
environmental conditions are forecast to be generally conducive for
development, the system’s proximity to the disturbance to the east
could inhibit the chances of formation. The low is forecast to move
slowly westward later this week.
* Formation chance through 48 hours…low…near 0 percent.
* Formation chance through 5 days…medium…40 percent.

Forecaster Roberts
Tropical Depression Jova Discussion Number 6
NWS National Hurricane Center Miami FL EP122017
200 AM PDT Sun Aug 13 2017

The center of Jova remains exposed based on GOES-16 shortwave
infrared imagery. Another strong burst of convection has developed
since 0300Z within 60 nmi southwest of the center, justifying the
maintenance of Jova as a tropical cyclone for this advisory. Two
ASCAT passes at 0443Z and 0529Z each indicated peak surface winds of
24 kt in the western semicircle. However, since the scatterometers
missed the eastern semicircle, the intensity will be maintained at
30 kt based on a Dvorak satellite estimate of 30 kt from TAFB.

The motion estimate remains westward, or 270/13 kt. The initial
position had to be adjusted southward slightly based on GOES-16
high-resolution imagery and the two ASCAT passes that just caught
the low-level circulation center. Otherwise, there is no significant
change to the previous forecast track or rationale. The deep-layer
subtropical ridge to the north of the cyclone is forecast by the
bulk of the NHC model guidance to remain intact, driving the cyclone
and its remnants westward to west-southwestward until the system
degenerates into an open trough in 3-4 days.

Intermittent short bursts of convection may continue to develop for
the next 12-18 h or so, but on the whole, there should be a general
decrease in both the intensity and coverage of any convection. By 24
hours and beyond, moderate easterly wind shear near 20 kt along with
decreasing mid-level moisture and marginal SSTs below 26C should
result in steady weakening and a gradual spin down of the
circulation. The official intensity forecast is similar to the
previous one and the consensus model IVCN, with remnant low status
expected in about 24 hours.

FORECAST POSITIONS AND MAX WINDS

INIT 13/0900Z 20.4N 116.0W 30 KT 35 MPH
12H 13/1800Z 20.4N 118.0W 25 KT 30 MPH
24H 14/0600Z 20.5N 120.4W 25 KT 30 MPH…POST-TROP/REMNT LOW
36H 14/1800Z 20.4N 122.7W 20 KT 25 MPH…POST-TROP/REMNT LOW
48H 15/0600Z 20.3N 124.9W 20 KT 25 MPH…POST-TROP/REMNT LOW
72H 16/0600Z 19.8N 129.4W 20 KT 25 MPH…POST-TROP/REMNT LOW
96H 17/0600Z…DISSIPATED

$$
Forecaster Stewart