[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 012042
TCDAT2

Tropical Depression Two Discussion Number   1
NWS National Hurricane Center Miami FL       AL022023
400 PM CDT Thu Jun 01 2023

Satellite imagery over the past 12-18 hours indicate that the area
of low pressure in the northeastern Gulf of Mexico has become better
organized. A burst of moderate to deep convection that initiated
last night has persisted into the afternoon with an increase in
banding, though the cloud tops have been warming recently. An
earlier ASCAT-C pass at 1558 UTC also indicated a broad closed
circulation had developed along the southern edge of the cirrus
canopy. The NOAA ship Ronald H. Brown passed very near the center
earlier, showing a distinct wind shift with west-southwest winds
just south of the center. An Air Force Reserve Reconnaissance
aircraft has been investigating the system this afternoon. So far,
the aircraft was able to close off a circulation, and found flight
level winds in the 35-40 kt range to the northeast of the center.
The most recent TAFB Dvorak fix provided a data-T number of
2.0/30-kt. Based on all the above data, the system has enough
organization to initiate advisories on Tropical Depression Two, with
maximum sustained winds of 30 kt.

The depression has been meandering today, with the estimated motion
at 290/2 kt. Currently, the steering currents over the system are
light and variable as the cyclone is positioned directly overhead of
an upper-level trough. However as this trough shifts eastward,
deep-layer flow out of the north-northwest should begin to move the
cyclone slowly to the south or south-southwest with gradually
increasing forward motion. The initial NHC forecast track has
elected to stay close to the reliable consensus aid TVCN, which is
pretty close to a blend of the latest GFS and ECMWF forecasts.

Intensity-wise, there is a small window for the system to intensify
further over the next 12-24 hours. While SHIPS diagnosed 200-850 mb
westerly shear is quite high, above 30 kt, with plenty of dry
mid-level air lurking to the west, the GOES-16 derived motion winds
suggest the cold cloud tops only extend up to 300 mb where westerly
flow is currently lighter. This factor may explain why upper-level
cirrus outflow has been expanding westward away from the center in
the northern semicircle. Sea surface temperatures between 26-27 C
combined with cold upper-level temperatures are also likely helping
to maintain enough thermodynamic instability for moderate to deep
convection to persist near the center. For this reason, the latest
NHC intensity forecast shows some modest intensification over the
next 12-24 h. However, by Friday night into Saturday, the same
northwesterly flow steering the system is also expected to rapidly
increase the shear as the system becomes positioned on the upstream
side of the upper-level trough, where subsidence may inhibit
additional convection. Thus, weakening is forecast to begin by
Friday night and the latest forecast degenerates the cyclone into a
remnant low by 60-h with dissipation shortly thereafter.

At this juncture, the relatively small wind field of the tropical
cyclone, combined with its motion keeping the center over the open
Gulf of Mexico for at least the next few days precludes the need
for any Watches and Warnings at this time.

Per the Public Information Statement that was issued by NHC on May
11, this system is being numbered as the second cyclone of 2023 in
the Atlantic basin and is being designated as Tropical Depression
Two.  During the course of typical re-assessment of weather systems
in the NHC's area of responsibility, NHC determined that an area of
low pressure that formed off the northeastern coast of the United
States in mid-January was an “unnamed” subtropical cyclone and was
given AL012023 as its system ID.  As a result, this system is
designated as AL022023, and advisories are being issued in AWIPS bin
2 (e.g., Public Advisories have been issued under AWIPS header
TCPAT2 and WMO header WTNT32 KNHC).  If Tropical Depression Two
becomes a tropical storm, it would be given the name `ARLENE`.


FORECAST POSITIONS AND MAX WINDS

INIT  01/2100Z 28.0N  86.6W   30 KT  35 MPH
 12H  02/0600Z 27.7N  86.7W   35 KT  40 MPH
 24H  02/1800Z 26.4N  86.6W   35 KT  40 MPH
 36H  03/0600Z 24.8N  86.2W   30 KT  35 MPH
 48H  03/1800Z 23.7N  85.7W   30 KT  35 MPH
 60H  04/0600Z 22.6N  84.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  04/1800Z...DISSIPATED

$$
Forecaster Papin

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