Hurricane John Forecast Discussion

263 
WTPZ45 KNHC 262039
TCDEP5

Hurricane John Discussion Number  16
NWS National Hurricane Center Miami FL       EP102024
300 PM CST Thu Sep 26 2024

John has slowed its forward motion this afternoon. A scatterometer 
pass late this morning confirmed that the motion had slowed and the 
center is lingering offshore. The inner core of convection has 
become less pronounced and the circulation may be feeling the 
orographic effects of the mountainous terrain of southwestern 
Mexico. However, a strong convective curved band extends in the 
southwest semi-circle. Dvorak satellite intensity estimates have 
remained fairly steady this afternoon between 65 to 75 kt. Given the 
current satellite intensity estimates, the initial intensity for 
this advisory remains at 65 kt.

The hurricane has not been moving much since the previous advisory 
and the estimated motion is 325/ 2 kt. This slow motion is forecast 
to continue as John approaches the coastline, moving along the 
coast or just inland later tonight or early tomorrow. Some of the 
global model fields keep the system offshore near the coast a 
little longer. In the long term, a turn back to the west-northwest 
is anticipated as the system weakens and is steered by a high 
pressure ridge located over northern Mexico.

The overall environment remains favorable for John to strengthen 
with very warm sea surface temperatures and low wind shear. 
However, John's proximity to the coastline may continue to disrupt 
the circulation and not allow for much additional strengthening. The 
latest NHC intensity forecast shows some slight strengthening over 
the next 12 h. Models are in fairly good agreement that steady 
weakening will begin Friday, with the system becoming a depression 
on Friday night.

John has a very large rain shield, and flooding impacts will extend
well outside where the system makes landfall. It cannot be
emphasized enough that catastrophic life-threatening flash flooding
and mudslides are expected to continue through the end of the week
for portions of the Mexican States of Guerrero and Michoacan.


KEY MESSAGES:

1. Hurricane John will bring additional very heavy rainfall to
coastal portions of southwest Mexico through Friday. The additional
rainfall totals will be falling across areas that have received very
heavy rainfall amounts over the past few days. This heavy rainfall
will likely cause significant and catastrophic life-threatening
flash flooding and mudslides to the Mexican States of Guerrero and
Michoacán.

2. John is forecast to continue strengthening up until landfall, and 
a Hurricane Warning is in effect along the coastline of southwestern 
Mexico, where hurricane conditions are imminent.  Tropical Storm 
Warnings are also in effect for portions of the area, where 
tropical storm conditions are ongoing or imminent.


FORECAST POSITIONS AND MAX WINDS

INIT  26/2100Z 17.6N 102.8W   65 KT  75 MPH
 12H  27/0600Z 18.0N 103.0W   70 KT  80 MPH
 24H  27/1800Z 18.6N 103.5W   40 KT  45 MPH...INLAND
 36H  28/0600Z 19.2N 104.7W   30 KT  35 MPH...OVER WATER
 48H  28/1800Z 19.8N 106.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 60H  29/0600Z 20.6N 107.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  29/1800Z...DISSIPATED

$$
Forecaster Kelly