Jul 25 Tuesday 2017

Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Tue Jul 25 2017

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

Tropical cyclone formation is not expected during the next 5 days.

$$
Forecaster Blake

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
500 AM PDT Tue Jul 25 2017

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

The National Hurricane Center is issuing advisories on Tropical
Storm Greg, located more than 1000 miles east of the Big Island of
Hawaii, on Hurricane Hilary, located a few hundred miles
south-southwest of Manzanillo, Mexico, and on recently upgraded
Hurricane Irwin, located several hundred miles southwest of the
southern tip of the Baja California peninsula.

1. An area of low pressure could form several hundred miles south of
Mexico in a day or two. Development, if any, of this system is
expected to be slow to occur for the next few days while it moves
west-northwestward at 5 to 10 mph. Upper-level winds could become
more conducive for some development by the weekend as Hurricane
Hilary moves farther away from the disturbance.
* Formation chance through 48 hours…low…near 0 percent.
* Formation chance through 5 days…low…30 percent.

Forecaster Blake

Hurricane Hilary Discussion Number 16
NWS National Hurricane Center Miami FL EP092017
300 AM MDT Tue Jul 25 2017

Hilary’s compact, symmetric, inner core continues to become better
defined on satellite imagery. Microwave imagery suggests
that the eye is quite small, less than 10 n mi in diameter, with
little evidence of vertical tilt of the vortex. The current
intensity estimate is now 90 kt in agreement with a Dvorak estimate
from the NESDIS SAB. Hilary should be in a moist air mass and over
a warm ocean for the next couple of days. Dynamical guidance
predicts some increase in northerly shear over the cyclone in 1- to
2-days, but probably not enough of an increase to impede at least
some additional strengthening. The official intensity forecast
calls for Hilary to become a major hurricane in 12 hours or so and
reach a peak in a day or so. This is in good agreement with the
latest Florida State University Superensemble (FSSE) prediction.
Later in the forecast period, gradually cooling sea surface
temperatures should induce slow weakening.

The initial motion estimate remains west-northwestward, or 290/9 kt.
A mid-tropospheric ridge extending westward from the southwestern
United States would cause Hilary to continue on its
west-northwestward track for the next several days. In a few days,
however, Hilary is likely to pass close to Hurricane Irwin. The
current thinking is that the circulation of Hilary will dominate so
that little influence on Hilary’s track, due to binary interaction
with Irwin, will occur. On the other hand, the latter tropical
cyclone is expected to begin rotating around Hilary’s circulation
later in the forecast period (please refer to the Forecast
Discussion on Irwin for additional information). The official track
forecast is quite close to the simple consensus TVCN, and to the
corrected consensus predictions, HCCA and FSSE.

FORECAST POSITIONS AND MAX WINDS

INIT 25/0900Z 15.3N 106.7W 90 KT 105 MPH
12H 25/1800Z 15.8N 108.2W 100 KT 115 MPH
24H 26/0600Z 16.3N 110.4W 105 KT 120 MPH
36H 26/1800Z 16.8N 112.6W 105 KT 120 MPH
48H 27/0600Z 17.4N 114.8W 100 KT 115 MPH
72H 28/0600Z 18.6N 118.7W 85 KT 100 MPH
96H 29/0600Z 19.5N 122.5W 75 KT 85 MPH
120H 30/0600Z 20.0N 126.0W 65 KT 75 MPH

$$
Forecaster Pasch

Hurricane Irwin Discussion Number 12
NWS National Hurricane Center Miami FL EP102017
200 AM PDT Tue Jul 25 2017

Deep convection associated with Irwin now wraps almost all of the
way around the center, and there have been occasional hints of a
eye in microwave and conventional satellite imagery. Subjective
satellite estimates from TAFB and SAB are just below hurricane
strength, while several objective estimates, including the CIMSS
satellite consensus, are above hurricane strength. With the attempts
at eye formation, the initial intensity will lean toward the higher
intensity estimates, and thus Irwin is upgraded to a hurricane.

The initial motion is a little more northward than before at 300/4.
A slow westward motion is forecast today as a weak mid-level ridge
remains in place to the north of the storm. A west-southwestward
motion is expected between 24-72 h as Hurricane Hilary approaches
from the east. After that, Irwin is expected to undergo an binary
interaction with Hilary, with the most likely result for Irwin
being a generally northward motion around the eastern semicircle of
Hilary. The details of this are still uncertain, with the ECMWF
and Canadian models merging the two cyclones before 120 h, while
the GFS and UKMET keep them separate until after 120 h. The new
track forecast is similar to the previous forecast through 72 h.
After that, it leans towards the GFS/UKMET in keeping the cyclone
separate and accelerating Irwin around the eastern side of Hilary.

Little change in strength is likely for the next 24 h. After that,
increasing shear associated with the outflow of Hilary is likely to
cause Irwin to weaken, although there is considerable spread in the
guidance as to how much shear and how much weakening. By the end
of the forecast period, cooler water along the forecast track and
proximity to Hilary should cause additional weakening. The new
forecast track is a slight adjustment of the previous track. An
alternative intensity scenario is that Irwin dissipates as it is
absorbed by Hilary before 120 h.

FORECAST POSITIONS AND MAX WINDS

INIT 25/0900Z 15.5N 118.7W 65 KT 75 MPH
12H 25/1800Z 15.3N 119.4W 65 KT 75 MPH
24H 26/0600Z 15.0N 120.5W 65 KT 75 MPH
36H 26/1800Z 14.6N 121.4W 60 KT 70 MPH
48H 27/0600Z 14.3N 122.2W 55 KT 65 MPH
72H 28/0600Z 14.0N 123.0W 55 KT 65 MPH
96H 29/0600Z 16.0N 122.5W 55 KT 65 MPH
120H 30/0600Z 20.0N 123.0W 50 KT 60 MPH

$$
Forecaster Beven

Tropical Storm Greg Discussion Number 32
NWS National Hurricane Center Miami FL EP072017
200 AM PDT Tue Jul 25 2017

Convection associated with Greg is currently very disorganized and
confined to the northwestern quadrant. The initial intensity
remains at 40 kt based on a blend of various satellite intensity
estimates. Greg is forecast to move into a drier air mass,
encounter increasing shear, and move over decreasing sea surface
temperatures during the next 48-72 h, and this combination should
result in the system degenerating to a remnant low during this
time. The new intensity forecast is changed little from the
previous forecast except to make the cyclone a remnant low at 48 h.

The initial motion is 295/8. Greg should move northwestward for
the next day or so on the south side of a low- to mid-level ridge.
After that, a turn to the west and then west-southwest is expected
when Greg becomes a shallow system and is steered by the low-level
trade wind flow. The NHC track forecast is again a little to the
north of the previous forecast and lies a little to the south
of the various consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT 25/0900Z 15.2N 135.7W 40 KT 45 MPH
12H 25/1800Z 16.0N 136.7W 35 KT 40 MPH
24H 26/0600Z 16.9N 137.9W 35 KT 40 MPH
36H 26/1800Z 17.5N 139.4W 30 KT 35 MPH
48H 27/0600Z 17.6N 140.8W 30 KT 35 MPH…POST-TROP/REMNT LOW
72H 28/0600Z 17.0N 144.0W 25 KT 30 MPH…POST-TROP/REMNT LOW
96H 29/0600Z 16.0N 146.5W 20 KT 25 MPH…POST-TROP/REMNT LOW
120H 30/0600Z 15.0N 149.5W 20 KT 25 MPH…POST-TROP/REMNT LOW

$$
Forecaster Beven