971
WTPZ42 KNHC 230253
TCDEP2

Hurricane Polo Discussion Number  10
NWS National Hurricane Center Miami FL       EP172026
900 PM CST Tue Sep 22 2026

The last few fixes this afternoon from the NOAA P-3 Hurricane Hunter
aircraft suggested that Polo was in the middle of an eyewall
replacement cycle (ERC). Flight level winds from the inner eyewall
had been decreasing in addition to rising pressures and somewhat
less pronounced warm core in the center. The secondary eyewall was
also seen on polar-orbiter imagery with a much larger eyewall taking
shape on both the SSMIS and WSFM microwave passes compared to this
morning. The satellite structure of Polo also looks less pristine
due to the ongoing ERC, with some erosion and expansion of the cold
cloud tops that surround the eye. Based on the earlier aircraft data
and evolution of satellite imagery since that time, the initial
intensity is being set at 145 kt this advisory, still making Polo a
very dangerous category 5 hurricane.

One-minute mesosector imagery over Polo has been very useful to
monitor its motion, and the inner eye of the storm has been
wobbling, with the best guess motion an northeastward drift at 45
degrees at 1 kt. The track guidance remains insistent that Polo will
soon undergo a slow but sharp turn to the northwest and
west-northwest as a deep-layer ridge centered over east Texas
continues to build in. In fact, the track guidance this cycle shows
even more of a leftward bend in 48-72 h as the ridge moves westward
with the hurricane. While the latest NHC track forecast is very
close to the prior one for the first 36 h, it is a little slower
given the current motion, and then further south and west beyond 36
h. This track will still take Polo close to, but just offshore of
the southwestern Mexican coast, where tropical storm conditions are
still expected. The latest NHC forecast lies closest to the Google
DeepMind ensemble mean (GDMI). Toward the end of the forecast
period, the ridge steering Polo is forecast to become eroded by a
combination of Tropical Storm Odalys located to its west, and a
digging mid-latitude trough moving into the western United States
coast. Thus, Polo will likely turn back northwestward or even
northward by the end of the forecast period, though this has also
been shifted west of the prior track following the leftward shift in
the guidance this cycle. There still remains significant uncertainty
in Polo`s track in the 4-5 day period.

Environmental conditions remain very favorable over Polo currently.
Vertical wind shear is forecast to remain below 10 kt for the next
24 h, with plenty of nearby deep-layer moisture. In addition, Polo
is over the warmest sea-surface temperatures in the basin, which
also extend vertically well below the surface, which should limit
ocean upwelling of the slow moving hurricane. However, the big
question mark is how the ongoing ERC will evolve in the next
12-24 h. The last few microwave images already show a larger closed
eyewall taking shape. There are also hints of the ERC successfully
completing in the next 24 h in the most recent raw output from the
18z HAFS-A run. Thus, the NHC intensity forecast shows some
short-term fluctuations in intensity both down and up over the next
24-36 h, though it is difficult to forecast these inner-core
structural changes with much confidence. SHIPS guidance thereafter
continues to indicate an increase in easterly shear as the ridging
overhead intensifies, and the NHC intensity forecast shows gradual
weakening beginning by that time, with a somewhat faster rate of
weakening now shown in days 4-5. However, this intensity forecast
remains on the high side of the guidance except for the HFIP
Corrected Consensus Approach (HCCA), which is a good 20-30 kt
higher than the rest of the guidance this cycle.


Key Messages:

1. Heavy rainfall associated with Polo will impact coastal portions
of southwest Mexico through Thursday. This rainfall may produce
life-threatening flooding and mudslides, especially in areas of
steep terrain.

2. A Tropical Storm Warning is in effect for portions of
southwestern Mexico, and the Tropical Storm Watch is in effect
westward to Playa Perula. Interests in these areas should closely
monitor updates to the forecast.


FORECAST POSITIONS AND MAX WINDS

INIT  23/0300Z 14.7N 101.3W  145 KT 165 MPH
 12H  23/1200Z 15.0N 101.6W  140 KT 160 MPH
 24H  24/0000Z 15.9N 102.8W  145 KT 165 MPH
 36H  24/1200Z 16.4N 104.3W  140 KT 160 MPH
 48H  25/0000Z 16.6N 106.1W  135 KT 155 MPH
 60H  25/1200Z 16.8N 108.0W  125 KT 145 MPH
 72H  26/0000Z 17.0N 110.0W  120 KT 140 MPH
 96H  27/0000Z 18.2N 112.7W  110 KT 125 MPH
120H  28/0000Z 20.9N 113.7W   95 KT 110 MPH

$$
Forecaster Papin