Update from the NHC on Gonzalo, Tropical Depression 8

From the National Hurricane Center:

Tropical Storm Gonzalo
Recently-obtained GCOM and WindSat microwave data from overnight
shows that Gonzalo's center is a little farther south than
previously estimated. In addition, the storm's structure has
become a little disheveled since yesterday, with the deep
convection losing some organization. SAB's data-T number responded
to this by falling to 2.5, but overall the CI numbers and SATCON
support maintaining 55 kt for now.

There is still an incredible amount of uncertainty in Gonzalo's
intensity forecast. Sea surface temperatures to the east of the
Windward Islands are warm--close to 29C--and the storm is likely to
be moving through an environment of relatively light shear at least
for the next 48 hours or so. The ambient environment is not
particularly moist, however, with mid-level relative humidity
generally around 50 percent, and it already appears that this dry
air is affecting Gonzalo. Small cyclones like Gonzalo tend to
succumb to any type of adverse environmental conditions quite
easily, and it's possible that the system could struggle during the
next couple of days. This is the solution shown by some of the
global models, particularly the ECMWF and UKMET. On the other
hand, the hurricane statistical and dynamical models, as well as
the GFS, continue to show Gonzalo strengthening to a hurricane
before it reaches the Windward Islands. Out of an abundance of
caution, the official forecast continues to show Gonzalo becoming a
hurricane in about 24 hours, but the uncertainty in this scenario
cannot be stressed enough. There is a higher degree of certainty
that Gonzalo would weaken once it moves over the eastern and
central Caribbean Sea, where even the GFS shows it opening up into
a wave.

Even with the southward adjustment of the initial position, Gonzalo
still appears to be moving westward, or 270/12 kt. The subtropical
ridge to the north is forecast to push Gonzalo toward the west or
west-northwest, with an increase in forward speed, for the entire
5-day forecast period. Much of the track uncertainty hinges on
exactly how strong Gonzalo gets, with the stronger model
representations showing the storm making more poleward process.
Models such as the ECMWF and UKMET, which keep Gonzalo weak or open
it up into a trough, are along the southern side of the guidance
envelope. The updated NHC track forecast has been shifted
southward some, to account for the new initial position and to be a
little closer to the intensity consensus, HCCA, and the Florida
State Superensemble.

Key Messages

1. There is an increasing risk of wind and rain impacts from
Gonzalo in portions of the southern Windward Islands this weekend,
however there is significant uncertainty in how strong Gonzalo will
be when it moves across the islands.

2. Despite the uncertainty in Gonzalo's future intensity, hurricane
conditions are possible across portions of the southern Windward
Islands. Hurricane Watches are currently in effect for Barbados
and St. Vincent and the Grenadines, and additional watches for
other islands could be required later today. Interests in the
southern Windward Islands should monitor the progress of Gonzalo and
follow any advice given by local officials.

FORECAST POSITIONS AND MAX WINDS

INIT 23/1500Z 9.6N 48.3W 55 KT 65 MPH
12H 24/0000Z 9.8N 50.0W 60 KT 70 MPH
24H 24/1200Z 10.1N 52.7W 65 KT 75 MPH
36H 25/0000Z 10.5N 55.7W 70 KT 80 MPH
48H 25/1200Z 11.2N 59.0W 70 KT 80 MPH
60H 26/0000Z 11.9N 62.3W 70 KT 80 MPH
72H 26/1200Z 12.6N 65.4W 65 KT 75 MPH
96H 27/1200Z 14.0N 71.4W 50 KT 60 MPH
120H 28/1200Z 15.5N 77.5W 40 KT 45 MPH

Tropical Depression 8
Satellite imagery indicates that the depression is getting better
organized, with a better-defined center located near the
northeastern end of a broadly curved convective band. Satellite
intensity estimates from TAFB and SAB have increased to 30 kt, and
that will be the initial intensity for this advisory. An Air Force
Reserve Hurricane Hunter aircraft is currently enroute to
investigate the depression.

The initial motion is west-northwestward or 285/8 kt. A mid-level
ridge over the central United States is the predominant steering
influence, and the global models forecast this ridge to build
during the several days. This should cause the depression to turn
more westward by 48-60 h and south of west after about 72 h. The
track guidance is in good agreement with that scenario, and the new
NHC forecast track, which has only minor adjustments from the
previous track, lies near the various consensus models. The new
forecast track has the center making landfall along the Texas coast
between 48-60 h.

The depression is in an environment of light shear and over warm
sea surface temperatures, so at least slow strengthening is
expected until landfall. The new intensity forecast, which lies a
little below the intensity consensus, now calls for a peak
intensity of 45 kt before landfall. Data from the Hurricane Hunter
will give more details on whether the structure of the cyclone has
improved or not, which will be incorporated into the next forecast
cycle.

Key Messages

1. The depression is expected to strengthen and it could bring
tropical-storm-force winds to portions of the Texas coast, where a
tropical storm watch is in effect.

2. The depression is expected to produce heavy rains along the Gulf
Coast from Louisiana to the Lower Texas Coast. These rains could
result in flash flooding and minor river flooding.

FORECAST POSITIONS AND MAX WINDS

INIT 23/1500Z 26.3N 90.7W 30 KT 35 MPH
12H 24/0000Z 26.7N 91.8W 30 KT 35 MPH
24H 24/1200Z 27.4N 93.4W 35 KT 40 MPH
36H 25/0000Z 27.8N 94.9W 40 KT 45 MPH
48H 25/1200Z 28.0N 96.5W 45 KT 50 MPH
60H 26/0000Z 28.0N 98.0W 40 KT 45 MPH...INLAND
72H 26/1200Z 27.9N 99.3W 30 KT 35 MPH...INLAND
96H 27/1200Z 27.5N 101.0W 20 KT 25 MPH...POST-TROP/INLAND
120H 28/1200Z 27.0N 103.0W 15 KT 15 MPH...POST-TROP/INLAND