564
WTNT44 KNHC 070857
TCDAT4

Tropical Storm Isaias Discussion Number 3
NWS National Hurricane Center Miami FL AL092026
400 AM CDT Wed Oct 07 2026

Satellite imagery depicts a bursting pattern with the tropical
cyclone this morning, with cloud top temperatures below -85 C in the
deep convection close to the estimated center. Earlier, an 0307 UTC
ASCAT-C pass suggested the low-level circulation was still rather
broad, with a peak wind retrieval of only 31 kt. However, the
bursting convection already appears to be tightening up the
circulation somewhat, with a nearby surface observation from a buoy
north of the center recently reporting a sustained 10 m adjusted
wind of 35 kt. This information is enough to upgrade the depression
to Tropical Storm Isaias for this advisory. This initial intensity
will be 35 kt, which also agrees with the 06 UTC Dvorak fix of
T2.5/35 kt. Both Air Force Reserve and NOAA Hurricane Hunter
reconnaissance missions are scheduled to sample the tropical storm
later today.

Isaias is estimated to be moving east-northeastward this morning at
075/7 kt. This general motion should continue today as the storm's
steering is influenced by a zonally oriented mid-level trough
currently draped along the northern Gulf coast. Over time, this
trough is expected to be reinforced by another short-wave that is
moving across the Rocky Mountains, with the trough ultimately
sharpening up northwest of Isaias over Texas. At the same time, a
subtropical ridge centered south of Bermuda is expected to shift
westward, helping to enhance the deep-layer southerly flow over the
eastern Gulf. Thus, Isaias is expected to turn northeastward and
then northward on Thursday and Friday, making its approach to the
northern Gulf coast in 60-72 h. As mentioned in the previous
discussion, there remains quite a bit of along and across-track
spread in the track guidance, with the AI-model guidance remaining
on the east side, and physics-based models on the west side of the
guidance envelope. The NHC track forecast continues to favor more of
the eastward solutions, but not quite as far east as the latest HFIP
Corrected Consensus Approach (HCCA) or Google DeepMind ensemble mean
(GDMI). This latest track is a eastward shift compared to the
previous forecast, but given large amount of across- and along-track
spread users should continue to monitor forecast updates given the below-average track confidence.

The short-term environment near Isaias is rather favorable, with
very warm 30-31 C sea-surface temperatures, plenty of deep-layer
moisture, with light to moderate shear diagnosed between 10-15 kt by
SHIPS guidance. While it is difficult to get an exact gauge on the
tropical storm's core structure since there have not been any
recent microwave images, it is worth noting both the 00 UTC HAFS-A/B
runs appeared to initialize with a broad structure similar to what
was noted in the earlier ASCAT pass. Despite their initial broad
structure, these hurricane-regional models show Isaias developing an inner-core rather quickly later today. There was a notable increase
in the intensity aid guidance this forecast cycle, and the NHC
intensity forecast is being raised accordingly, now showing Isaias
reaching a peak intensity of 95 kt in 48 h while it is over the
central Gulf. Vertical wind shear then increases quite dramatically
in the final 24 hours before the cyclone reaches the northern Gulf
coast, though it is looking more likely that Isaias will be a
significant hurricane when it reaches the coast. Near landfall,
Isaias will also be interacting with the short-wave trough, likely
leading to an expanding wind field. Additional convective and
motion asymmetries will likely cause rain and wind impacts to
extend far from the center on the eastern side of the storm.

Key Messages:

1. There is an increasing risk of dangerous wind and storm surge
impacts along portions of the northern Gulf Coast. Residents from
Louisiana to the Florida Panhandle should closely monitor the latest
forecast updates and ensure they have their hurricane plan in place.
Hurricane and Storm Surge Watches will likely be required for a
portion of the northern Gulf coast later today.

2. Tropical Storm Isaias will bring areas of heavy rainfall to the
central U.S. Gulf coast and much of the Southeast Friday into the
weekend. Flash and urban flooding, along with isolated river
flooding, will be possible.

3. Yucatan Peninsula of Mexico: Tropical Storm Isaias is expected to
strengthen and could bring gusty winds and areas of heavy rain to
the western portion of the Yucatan Peninsula over the next day or
two.


FORECAST POSITIONS AND MAX WINDS

INIT 07/0900Z 22.0N 94.1W 35 KT 40 MPH
12H 07/1800Z 22.2N 92.9W 50 KT 60 MPH
24H 08/0600Z 22.7N 91.4W 65 KT 75 MPH
36H 08/1800Z 23.9N 89.7W 80 KT 90 MPH
48H 09/0600Z 25.5N 88.5W 95 KT 110 MPH
60H 09/1800Z 27.7N 87.7W 90 KT 105 MPH
72H 10/0600Z 30.8N 87.7W 75 KT 85 MPH...INLAND
96H 11/0600Z 38.2N 87.5W 25 KT 30 MPH...POST-TROP/INLAND
120H 12/0600Z...DISSIPATED

$$
Forecaster Papin


= = = = = = =
To unsubscribe from WX-ATLAN and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-ATLAN.
--- scorpsmtpd
* Origin: capitolcityonline.net * KY, USA (1:2320/107)