[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 042051
TCDAT1

Tropical Depression Sixteen Discussion Number   2
NWS National Hurricane Center Miami FL       AL162017
500 PM EDT Wed Oct 04 2017

Visible satellite images show that the depression has lots of
curved bands, although it is somewhat lacking any inner core
features. An Air Force Reserve Hurricane Hunter flew into the
depression this afternoon and found a well-defined circulation, with
maximum flight-level winds of 37 kt and SFMR values around 30 kt.
These data support keeping the intensity at 30 kt for this advisory.

Environmental conditions look quite favorable for strengthening over
the next few days, with low shear and very warm and deep water in
the path of the cyclone.  The various rapid intensification indices
are all higher than the last cycle, suggesting an increasing chance
of rapid intensification occurring.  The fly in the ointment,
however, is all of the potential land interaction, first over
Central America and then possibly over the Yucatan Peninsula.  As
a compromise, the intensity forecast is raised considerably from the
previous one during the first 3 days, but is still below some
guidance, such as the HWRF.

The depression continues to move slowly northwestward, steered by a
distant ridge over the southwestern Atlantic.  However the steering
pattern is forecast to change quickly tomorrow as a mid-tropospheric
trough over the Florida Straits moves across the northwestern
Caribbean into the southwestern Gulf of Mexico.  Southerly flow on
the eastern side of that trough should cause the cyclone to move
much faster to the north-northwest by Friday and northward into the
Gulf of Mexico on Saturday.  While there is some agreement on the
synoptic pattern, the model track agreement is rather poor, even in
the short term, with the GFS and ECMWF being 90 miles apart on the
forecast track as soon as 24 hours out.  This has profound
differences down the road, with the GFS-based guidance moving
considerably faster and to the left of the ECMWF and UKMET across
the Gulf of Mexico.  Overall, the guidance has generally shifted a
bit westward since the last cycle, so the latest points in the long
range have been adjusted in that direction.  At this point, I
wouldn't focus too much attention on the details of the long-range
forecast until the guidance comes into better agreement.  A G-IV
mission and Florida special soundings have been set up for tomorrow
to better determine the synoptic steering flow around the cyclone.

KEY MESSAGES:

1. The depression is forecast to strengthen and bring tropical storm
conditions to portions of Nicaragua and Honduras tonight through
Friday.  Heavy rainfall could produce life-threatening flash
flooding and mud slides in portions of Nicaragua, Honduras, Costa
Rica, and Panama through Friday night.

2. The system is expected to be near hurricane intensity when it
approaches the Yucatan Peninsula late Friday or Saturday, bringing
direct impacts from wind, storm surge, and heavy rainfall.  A
hurricane watch could be issued for this area later this evening.

3. The system is forecast to continue strengthening over the Gulf of
Mexico and could affect portions of the northern Gulf Coast as a
hurricane this weekend, with direct impacts from wind, storm surge,
and heavy rainfall.  However, it is too early to specify the timing,
location, or magnitude of these impacts.  Residents along the Gulf
Coast from Louisiana to Florida should monitor the progress of this
system for the next several days and heed any advice given by local
officials.


FORECAST POSITIONS AND MAX WINDS

INIT  04/2100Z 12.5N  82.5W   30 KT  35 MPH
 12H  05/0600Z 13.2N  83.1W   40 KT  45 MPH
 24H  05/1800Z 14.6N  83.8W   40 KT  45 MPH...INLAND
 36H  06/0600Z 16.7N  84.6W   50 KT  60 MPH
 48H  06/1800Z 19.5N  85.8W   60 KT  70 MPH
 72H  07/1800Z 25.0N  88.0W   75 KT  85 MPH
 96H  08/1800Z 30.5N  86.0W   65 KT  75 MPH...INLAND
120H  09/1800Z 35.5N  82.0W   30 KT  35 MPH...POST-TROP/INLAND

$$
Forecaster Blake
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