Potential Tropical Cyclone Eighteen Forecast Discussion

588 
WTNT43 KNHC 040258
TCDAT3

Potential Tropical Cyclone Eighteen Discussion Number   2
NWS National Hurricane Center Miami FL       AL182024
1000 PM EST Sun Nov 03 2024

The convective structure of the system in the south-central 
Caribbean Sea has not become any better organized this evening. 
Current shower and thunderstorm activity is clustered in two regions 
to the south and northeast of the estimated center. The center 
itself remains quite broad and lacks distinct banding features, as 
seen on an earlier GMI microwave pass at 2219 UTC. Given the lack of 
improvement from this afternoon, the system remains a Potential 
Tropical Cyclone (PTC), with an initial intensity at 30 kt. An Air 
Force Reconnaissance Aircraft is in route to sample the system 
tonight, and we should soon also receive an ASCAT-B scatterometer 
pass to provide more information on its structure and intensity.

My best guess is that the system continues to move slowly northward
this evening, with a current motion a fairly uncertain 360/5 kt.
Over the next couple of days, a large mid-level ridge currently
parked north of the system off the southeastern U.S. coast should
shift a little eastward and build farther southeastward towards
Hispaniola. The result of this synoptic pattern should cause PTC18
to turn northwestward and gradually accelerate as it moves into the
northwestern Caribbean. This motion should bring the system near
Jamaica by Monday evening and the Cayman Islands on Tuesday evening.
This northwestward track should continue, likely bringing the system
over Cuba and ultimately into the southeastern Gulf of Mexico in 72
h. After that time, the track guidance begins to diverge, with
notable ECMWF ensemble cross-track spread in the
southwest-to-northeast direction over the Gulf of Mexico. Some of
this track spread is related to how fast a mid-latitude cutoff low
over the four corners region of the U.S. ejects out into the central
Plains. This feature will play a role in how much the mid-level
ridging ahead of the system becomes eroded when it emerges into the
Gulf of Mexico. The track guidance is a little slower compared to
the previous cycle, and the NHC track forecast is also a little bit
slower this advisory, while nudged just a hair to the west of the
prior forecast at the end of period. However, forecast confidence on
the track in the 96-h and 120-h time-frame is lower than usual.

The intensity forecast is also uncertain, because how much the
system is able to intensify will be determined by its evolving
structure over the next couple of days. Environmental conditions in
the northwestern Caribbean are forecast to be quite favorable, with
SHIPS guidance indicating vertical wind shear remaining 10 kt or
lower while traversing very warm 29-30 C sea-surface temperatures
for the next 48-60 h. Such an environment could favor rapid
intensification, as some of the regional-hurricane model guidance
aids were suggesting earlier today. However, this evolution depends
on when or if the system is able to develop an inner-core, and the
current poor structure argues against substantial development in the
short-term. Assuming the system does ultimately develop a better
aligned vortex, more significant intensification is forecast in the
24-60 h time frame, and the NHC intensity forecast still shows the
system becoming a hurricane in the northwestern Caribbean. After
PTC18 crosses Cuba into the Gulf of Mexico, the forecast environment
becomes less favorable, with increasing southwesterly shear and
decreasing sea-surface temperatures, though this environment is
quite dependent on the forecast track. The latest NHC intensity
forecast is quite similar to the prior one, splitting the difference
between the more aggressive hurricane-regional models, and more
subdued global model and statistical-dynamical aids.


Key Messages:

1. The disturbance is expected to become a tropical storm Monday and
pass near Jamaica on Monday night and Tuesday where a Tropical Storm
Warning is in effect. The system is forecast to become a hurricane
by Tuesday night and there is a risk of dangerous impacts from
hurricane-force winds and storm surge in the Cayman Islands and
portions of Cuba.

2. Interests in Cuba and the Florida Keys should closely monitor
this system as hurricane and tropical storm watches could be
required for portions of these areas on Monday.

3. The system is forecast to enter the western Gulf of Mexico later
this week, but given significant uncertainties in the long-range
forecast track and intensity, it is too soon to determine what, if
any, impacts could occur. Residents in this area should regularly
monitor updates to the forecast.

4. The system will bring areas of heavy rain across portions of the
western Caribbean, including Jamaica and the southern and western
portions of Cuba through mid-week. Flooding could occur over
portions of Jamaica and Cuba, with mudslides possible. Heavy
rainfall could then spread northward into Florida and adjacent
areas of the Southeast United States during the middle to late
portions of the week.


FORECAST POSITIONS AND MAX WINDS

INIT  04/0300Z 13.3N  76.9W   30 KT  35 MPH...POTENTIAL TROP CYCLONE
 12H  04/1200Z 14.2N  76.9W   35 KT  40 MPH...TROPICAL CYCLONE
 24H  05/0000Z 16.0N  77.6W   40 KT  45 MPH
 36H  05/1200Z 17.9N  78.9W   50 KT  60 MPH
 48H  06/0000Z 19.8N  80.9W   60 KT  70 MPH
 60H  06/1200Z 21.8N  82.9W   70 KT  80 MPH
 72H  07/0000Z 23.5N  84.5W   65 KT  75 MPH
 96H  08/0000Z 25.5N  87.0W   65 KT  75 MPH
120H  09/0000Z 26.5N  89.0W   55 KT  65 MPH

$$
Forecaster Papin