Tropical Depression Nine Forecast Discussion Number 1

By | September 23, 2022
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Tropical Depression Nine Discussion Number   1...Corrected
NWS National Hurricane Center Miami FL       AL092022
500 AM AST Fri Sep 23 2022

Corrected locations of convection in first paragraph. 

Convection this morning has increased primarily to the west of the 
area of low pressure we have been monitoring in the central 
Caribbean Sea, currently passing by to the north of Curacao island. 
The system already possessed a well-defined circulation for the last 
12 to 18 hours, but it was only overnight that the ongoing 
convective activity was able to persist long enough near the center 
to be considered a tropical cyclone. The most recent satellite 
intensity estimate from TAFB was up to T2.5/35-kt. However the 
GOES-16 derived motion winds from the meso sector over the system 
have only been 25-30 kt in the 925-850 mb layer on the northeastern 
periphery of the circulation. In addition, buoy 42059 located to the 
northeast of the center has been reporting winds up to only 27-kt. 
The combination of all these data provide enough justification to 
upgrade this system to Tropical Depression Nine, with the initial 
winds set at 30 kt for this advisory. An Air Force Reserve 
Reconnaissance mission will be investigating the system later this 
morning to provide more in-situ information of the system's 
structure and intensity.

The current motion right now is estimated to be off to the 
west-northwest at 290/12 kt. In the short-term, the depression is 
forecast to bend back more westward as a narrow east-to-west 
oriented mid-level ridge builds in behind the weakness left behind 
from Fiona. The current westward displaced convection may also tug 
the broad center in that direction as well. However, after 48 hours, 
this ridge will start to decay as a longwave deep-layer trough over 
the eastern United States begins to amplify southward. This synoptic 
evolution should then allow the cyclone to begin gaining latitude, 
though the exact timing at which this occurs could be somewhat 
related to the vertical depth of the cyclone and how it interacts 
with a weak upper-level trough expected to be over the far western 
Caribbean in the day 3-4 time-frame. The model guidance early on is 
in fairly good agreement, but larger across-track spread begins to 
take shape by 48 hours, with the GFS and its ensemble mean located 
further south and west, and with the ECMWF and its ensemble mean 
located further north and east. The initial track forecast has 
decided to split the difference between these two model suites, and 
lies fairly close to the consensus aids TVCN and HCCA. There is 
still a healthy amount of uncertainty in the track forecast at the 
day 4-5 timeframe. 

Currently the structure of the depression is quite disheveled, with
the low-level circulation mostly exposed, with deep convective
activity displaced to its west-southwest. This structure is due to
25-30 kt of northeasterly 200-850 mb vertical wind shear caused from
the equatorward outflow channel of Fiona, resulting in significant
upper-level flow over the system. However, as the depression moves
westward, it will move out form under this unfavorable flow and into
a lighter upper-level northeasterlies. However, it may take time for
the low-level center to become better aligned with the convective
activity, and thus only slow intensification is forecast over the
next 24-48 hours. After that period, most of the guidance shows
environmental conditions becoming much more favorable as shear drops
under 10 kt and the cyclone is over the warm 29-30 C waters of the
northwestern Caribbean. Thereafter, potential land interaction with
Cuba, and the potential for an increase in southerly shear at
day 5 may cap off the intensity at the end of the forecast. The
initial NHC forecast shows the depression intensifying up to a
category 2 hurricane by the time it nears the coast of Cuba.


Key Messages:

1. Tropical Depression Nine is expected to produce heavy rainfall 
and instances of flash flooding and possible mudslides in areas of 
higher terrain in Aruba, Bonaire, and Curacao. Heavy rains are also 
likely to spread into Jamaica and the Cayman Islands in the coming 
days. 

2. The depression is expected to approach Jamaica and the Cayman
islands as an intensifying tropical storm. Watches and warnings for
these locations may be required in subsequent forecast cycles.

3. This system is forecast to approach western Cuba and enter the
southeastern Gulf of Mexico by the end of the forecast period.
Interests in Cuba and those along the Eastern Gulf Coast of the
United States should closely monitor this system, though at this
juncture forecast uncertainty remains fairly high.


FORECAST POSITIONS AND MAX WINDS

INIT  23/0900Z 13.9N  68.6W   30 KT  35 MPH
 12H  23/1800Z 14.4N  70.2W   35 KT  40 MPH
 24H  24/0600Z 14.7N  72.6W   35 KT  40 MPH
 36H  24/1800Z 14.8N  75.0W   35 KT  40 MPH
 48H  25/0600Z 15.5N  77.1W   40 KT  45 MPH
 60H  25/1800Z 17.0N  78.8W   55 KT  65 MPH
 72H  26/0600Z 18.9N  80.5W   65 KT  75 MPH
 96H  27/0600Z 22.6N  82.6W   90 KT 105 MPH...NEAR CUBA
120H  28/0600Z 26.0N  82.3W   95 KT 110 MPH

$$
Forecaster Papin

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