Tropical Storm Polo

000
WTPZ42 KNHC 210848
TCDEP2
 
Tropical Storm Polo Discussion Number   3
NWS National Hurricane Center Miami FL       EP172026
300 AM CST Mon Sep 21 2026
 
Deep convection associated with Polo has been gradually increasing 
over the past several hours. A recent GMI microwave pass indicates 
that Polo is developing a small core, which is an early indication 
that significant strengthening could be beginning. The latest 
satellite intensity estimates range from 35 to 45 kt, and based on 
that data and an earlier ASCAT pass, the initial intensity is 
increased to 40 kt.

Environmental conditions appear very conducive for strengthening 
with the vertical wind shear expected to be less than 10 kt, 
mid-level humidities near or above 70 percent, and SSTs above 30 C 
during the next several days. These conditions, along with Polo's 
improving and compact structure, support rapid intensification. In 
fact, the SHIPS Rapid Intensification indices indicates that there 
is a near 90 percent chance of an increase in winds of at least 55 
kt over the next 48 hours. The NHC intensity forecast is quite 
aggressive and calls for rapid intensification, and shows Polo 
becoming a hurricane later today and a major hurricane on Tuesday. 
This prediction is higher than the previous one, but below the 
latest HCCA guidance which shows Polo reaching category 5 status in 
about 48 hours. 
 
The storm will likely drift eastward or southeastward during the 
next day or so in weak steering currents. However, a sharp turn to 
the west-northwest or northwest is expected by late Tuesday when a 
mid-level ridge becomes established to the northeast of Polo. This 
pattern should bring the core of the storm near the coast of 
southwestern Mexico on Wednesday and Thursday, and then well south 
of the Baja California Peninsula on Friday. There is a very large 
spread in the model solutions in where, when, and how sharply Polo 
makes the turn. The GFS model is on the far south side of the 
guidance envelope while the Google DeepMind ensemble mean is on the 
northern edge. The NHC track forecast has been nudged northward, and 
is in best agreement with the corrected consensus HCCA model. It 
should be noted that given the complex steering pattern and model 
spread, confidence in the details of the track forecast is quite 
low.
 
Key Messages:

1. Heavy rainfall associated with Tropical Storm Polo will impact 
coastal portions of southwest Mexico this week. This rainfall may 
produce life-threatening flooding and mudslides, especially in areas 
of steep terrain.
 
2. Polo is forecast to strengthen to a major hurricane while it 
moves closer to the coast of southwestern Mexico during the next few 
days. Although the core of the hurricane is forecast to stay 
offshore, it is too soon to determine the exact location or 
magnitude of impacts. Residents in southwestern Mexico should 
closely monitor its progress and updates to the forecast. A Tropical 
Storm Watch has been issued for portions of southwestern Mexico.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/0900Z 15.5N 103.8W   40 KT  45 MPH
 12H  21/1800Z 15.5N 103.1W   60 KT  70 MPH
 24H  22/0600Z 15.3N 102.5W   80 KT  90 MPH
 36H  22/1800Z 15.3N 102.0W  100 KT 115 MPH
 48H  23/0600Z 15.9N 102.4W  115 KT 130 MPH
 60H  23/1800Z 16.6N 103.0W  125 KT 145 MPH
 72H  24/0600Z 17.5N 104.1W  125 KT 145 MPH
 96H  25/0600Z 18.7N 106.6W  120 KT 140 MPH
120H  26/0600Z 19.8N 109.0W  115 KT 130 MPH
 
$$
Forecaster Cangialosi/Kelly