[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 080852
TCDAT3

Tropical Storm Julia Discussion Number   8
NWS National Hurricane Center Miami FL       AL132022
500 AM EDT Sat Oct 08 2022

Julia is a strengthening tropical cyclone. Satellite imagery has
shown an increase in persistent and deep convection occurring over
the center, with an expanding area of cloud top temperatures colder
than -80 deg C. Overnight data from the Air Force Hurricane Hunters
indicated the vertical structure of Julia is still organizing, with
evidence of multiple low-level centers noted in the 850-mb flight
level wind data. But, the aircraft reported flight-level winds of
59 kt and believable SFMR retrievals of 45-50 kt on its last pass
through the northeastern quadrant of the cyclone. Based on these
data, the initial intensity is set at 50 kt for this advisory.

Weak deep-layer shear, abundant mid-level moisture, and SSTs around
29.5 degrees Celsius appear conducive for steady to rapid
intensification of Julia during the next 24 h as it approaches
Central America. In fact, the SHIPS Rapid Intensification Index
shows a 63 percent chance of a 30 kt increase in intensity during
the next 24 h. Given the strengthening noted tonight and the
improved satellite structure, the NHC forecast calls for Julia to
rapidly intensify into a hurricane later today and continue
strengthening through landfall on Sunday. This forecast lies
between the multi-model consensus aids and the stronger SHIPS and
LGEM guidance. After landfall, the cyclone is forecast to weaken as
it moves across the terrain of Central America.

The estimated initial motion is westward at 265/16 kt. Julia is
expected to continue moving quickly westward for the next day
or so along the southern periphery of a strong mid-level ridge to
its north. This motion should bring the center of Julia near San
Andres and Providencia Islands this evening and over the coast of
Nicaragua within the warning area early Sunday. Based on a
southward shift in the track guidance, the NHC forecast has been
adjusted in that direction to bring it closer to the multi-model
consensus. As a result, the government of Nicaragua has extended
Hurricane and Tropical Storm Warnings southward along the coast.

There is still above average uncertainty regarding the future of
Julia after landfall. While some models (HWRF, HMON, GFS) show the
center largely remaining over land and dissipating, others (ECMWF
and UKMET) show low-level vorticity associated with Julia or its
remnants emerging over the eastern Pacific waters early next week.
While it appears unlikely that the surface circulation would survive
the topography of Nicaragua, this scenario could become more likely
if there are additional southward adjustments to the track. For now,
the NHC forecast shows weakening and dissipation by 72 h near the
coast of Central America, but interests along the Pacific coasts of
El Salvador, Honduras, and Nicaragua should monitor forecast
updates. Regardless, the set up is likely to lead to heavy rains
over Central America for several days, which could cause
life-threatening flash floods and mudslides, especially in areas of
mountainous terrain.


Key Messages:

1. Julia is forecast to strengthen into a hurricane later today, and
a Hurricane Warning is in effect for portions of the Nicaragua coast
and the islands of Providencia and San Andres. Hurricane-force winds
and a dangerous storm surge are expected in areas where the core of
the system crosses the islands tonight and moves onshore in
Nicaragua on Sunday.

2. Life-threatening flash flooding and mudslides are expected across
portions of Central America this weekend. Flash flooding is possible
across the Isthmus of Tehuantepec in Mexico early next week.


FORECAST POSITIONS AND MAX WINDS

INIT  08/0900Z 12.7N  78.0W   50 KT  60 MPH
 12H  08/1800Z 12.6N  80.4W   65 KT  75 MPH
 24H  09/0600Z 12.5N  82.9W   80 KT  90 MPH
 36H  09/1800Z 12.7N  85.2W   50 KT  60 MPH...INLAND
 48H  10/0600Z 13.2N  87.8W   35 KT  40 MPH...NEAR THE COAST
 60H  10/1800Z 13.8N  89.9W   30 KT  35 MPH...POST-TROP/INLAND
 72H  11/0600Z...DISSIPATED

$$
Forecaster Reinhart
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