[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 150851
TCDAT1

Hurricane Iota Discussion Number   8
NWS National Hurricane Center Miami FL       AL312020
400 AM EST Sun Nov 15 2020

Iota has continued to rapidly intensify, strengthening 35 kt during
the past 24 hours. Deep convection has increased in vertical depth
and has also expanded, producing a symmetrical Central Dense
Overcast (CDO) with a large area of cloud tops colder than -80C
surrounding the center. Upper-level outflow has also improved in all
quadrants as the deep-layer vertical wind shear has finally abated.
An Air Force Reserve reconnaissance investigating Iota early this
morning measured a peak 700-mb flight-level wind speed of 76 kt on
its outbound leg, which equates to about a 68-kt equivalent surface
wind speed. The second center dropsonde pressure was 987 mb with a
21-kt surface wind, which equals about 985 mb, a pressure drop of 4
mb in a little more than an hour. Based on these data, the intensity
has been increased to 70 kt for this advisory.

Iota has recently wobbled to the northwest, but the best motion
estimate is 280/05 kt. An expansive ridge extending westward from
the Atlantic across Florida and over the Gulf of Mexico will keep
Iota moving in a westward to west-northwestward motion for the next
few days, resulting in a Central America landfall in about 48 hours,
close to where former Hurricane Eta made landfall earlier this
month. As low-level ridging increases southward across the Gulf of
Mexico on days 3 and 4, Iota is expected to move westward farther
inland over Central America and dissipate by day 5. The new NHC
model guidance remains in good agreement on this developing track
scenario. The new official track forecast is a little north of the
previous advisory track, primarily due to the more northward initial
position, and lies along the southern edge of the guidance between
the consensus models TVCN, NOAA-HCCA, and FSSE.

The atmospheric and oceanic conditions are expected to be very
conducive for continued rapid strengthening, characterized by low
shear less than 5 kt, moist mid-tropospheric air, and sea-surface
temperatures of 28.5-29.0 deg C. Therefore, rapid intensification is
explicitly forecast for the next 48 hours, with Iota expected to
become a category 4 hurricane before it reaches central America. The
official intensity forecast is very similar to the bulk of the
intensity guidance, but lies a little below the Decay-SHIPS and LGEM
models, which bring Iota to 120-125 kt just prior to landfall. The
slightly lower intensity is due to the warm water east of Nicaragua
becoming a more shallow, which could result in some cold some
upwelling, plus a possible eyewall replacement cycle (ERC)
occurring. After Iota moves inland, rapid weakening is forecast as
the hurricane moves over the rugged terrain of Nicaragua and
southern Honduras. The new NHC intensity forecast is similar to a
blend of the IVCN, HCCA, and FSSE consensus models.


Key Messages:

1. Iota is expected to rapidly intensify and be a major hurricane
when it approaches the coast of Central America.  A Hurricane
Warning has been issued for portions of the coast of Nicaragua and
Honduras, and hurricane conditions and a dangerous storm surge are
expected there beginning Monday.

2.  Hurricane conditions are expected and storm surge impacts
are possible on Providencia beginning late Sunday night.  Tropical
storm conditions are expected and hurricane conditions are
possible by Sunday evening on San Andres.

3. Through Thursday, heavy rainfall from Iota will likely lead to
life-threatening flash flooding and river flooding across portions
of northern Colombia and Central America. Flooding and mudslides in
Honduras and Nicaragua could be exacerbated by Hurricane Eta’s
recent effects there, resulting in significant to potentiallycatastrophic impacts.


FORECAST POSITIONS AND MAX WINDS

INIT  15/0900Z 13.1N  77.3W   70 KT  80 MPH
 12H  15/1800Z 13.4N  78.4W   80 KT  90 MPH
 24H  16/0600Z 13.7N  80.1W   95 KT 110 MPH
 36H  16/1800Z 14.1N  81.7W  110 KT 125 MPH
 48H  17/0600Z 14.3N  83.1W  115 KT 130 MPH
 60H  17/1800Z 14.3N  84.4W   65 KT  75 MPH...INLAND
 72H  18/0600Z 14.2N  85.7W   35 KT  40 MPH...INLAND
 96H  19/0600Z 13.9N  88.7W   20 KT  25 MPH...INLAND
120H  20/0600Z...DISSIPATED

$$
Forecaster Stewart

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