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Tropical Storm IAN – Forecaster Discussion 

IAN – Public Advisories

AL092022 6 COR

1100 PM EDT SUN SEP 25 2022

Corrected grammatical error in motion discussion section.

All data available indicates that Tropical Storm Ian has begun the
well-anticipated rapid intensification. Data from a NOAA Hurricane
Hunter aircraft that was previously investigating Ian indicates the
cyclone has sustained winds now of 65 mph, which holds a 15 mph
difference than 18 UTC. The same aircraft also measured a pressure
between 991-989 mb, I will set the pressure at 989 mb. Satellite
imagery also shows Ian is becoming better organized with the coldest
cloud tops (~ -80 C) forming over the center and Ian becoming more
circular like a classic tropical cyclone.

Aircraft data indicates Ian has begun a northwestward motion of
around 10 kt, this motion is forecast to continue through the
overnight and then a north-northwestward motion is expected
Monday evening once the system approaches or makes landfall over
Cuba. There continues to be a fork in the road after day 2 on the
model guidance with half the envelope taking Ian over towards the
Apalachee Bay and the other half with with a potential landfall just
south of Tampa Bay. The track between days 3 and 5 will highly
depend on the strength and position of an upper-level trough located
over Central Appalachians. Past day 2, the track uncertainty is
higher than average and the forecast track could change based on
real-time trends before Wednesday. THN's track has been nudged
eastward again following the TVCN multi-model consensus aids, which
brings Ian into Tampa Bay by the end of Day 4.

As mentioned in the summary section, Ian seems to becoming rapidly
better organized with colder cloud tops encompassing the center of
circulation as well as starting to look more like a classic tropical
cyclone on IR satellite imagery. Ian is now moving into an area of
extremely warm ocean temperatures around 30-35 degrees C, this area
also virtually has no vertical wind shear that would disrupt the
core. Based on this, Ian has begun or will begin rapid
intensification shortly. SHIPS Rapid Intensification Index data
shows a potential 45 kt intensification within a 36 hour period, and
real-time data agrees this is the likely outcome. Ian will likely
become a hurricane sometime overnight or by late Monday morning. It
is very well possible depending on the timing of the intensification
period that Ian could also become a major hurricane late Monday, but
THN forecast calls for Ian to obtain category 3 status in just under
34 hours. Just as the track forecast deviates past day 2, so does
the intensity forecast. By day 3, as the upper-level trough digs
there will be an increase of shear which would ultimately cause Ian
to rapidly weaken prior to a landfall between the Florida panhandle
and Florida peninsula. After day 3, Ian will begin moving inland and
will continue to gradually weaken but forecast to remain
near-hurricane strength as the cyclone approaches the Florida and
Georgia state line. THN intensity forecast lies between SHIPS
consensus aids and NVGM dynamic model.

Regardless of the current intensity and track forecast, Ian is posed
to make a significant impact to the Gulf coast of Florida. Ian's
winds will expand further from the center of circulation or eye,
which is forecast to create a potentially catastrophic storm surge.
Interests along the entire Gulf coast of Florida should begin to
enact their hurricane plans tonight.

Key Messages:

1. While Ian is forecast to move into the Gulf of Mexico on Tuesday
as a strong major hurricane, there uncertainty remains high on where
Ian will make landfall later this week. Residents and tourists from
St. Marks to Fort Myers should closely monitor Ian and begin their
hurricane plans now. Ian has the potential to drive a catastrophic
storm surge, extreme winds, and flood-resulting rainfall.

2. Life-threatening storm surge of near 14 feet are expected to
impact western Cuba on Monday. Residents should immediately evacuate
the coast and complete all life-saving and property-saving efforts
tonight as tropical conditions will begin to on-set overnight.

3. Tropical storm conditions are expected across the lower Florida
Keys on Tuesday and tropical storm conditions are possible along
southwestern portions of the Florida peninsula.

Forecaster Latteri