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FXCA20 KWBC 251905
PMDCA

Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
304 PM EDT Fri Sep 25 2026

Forecast Bulletin 25 September 2026 at 1900 UTC:

Mexico and Northern Central America . . .
The Central American Gyre (CAG) is present south of Mexico over
the Pacific, supporting high levels of precipitable water (PW)
over the southern Mexican Pacific coast to El Salvador, helping to
transport moisture from the Caribbean over the Yucatan Peninsula,
Belize, and Guatemala. A tropical wave will move over northern
Central America and southern Mexico to favor low-level moisture
convergence, while upper-level divergence will support the
development of deep convective storms this afternoon. Rainfall
accumulation maxima of 15-25 mm are expected over this region. The
CAG will move westward over the next few days, supporting
continuous moisture transport over the region, and will approach
southwestern Mexico by Sunday, enhancing rainfall totals to 20-35
mm. The tropical wave will continue moving slowly over Guatemala
and southern Mexico, interacting with the enhanced PW associated
with the CAG circulation to trigger thunderstorms from eastern
Honduras to the Isthmus of Tehuantepec over the weekend.
A mid-level ridge extending from southern Texas to southern Baja
California will maintain a southerly flow that transports moisture
from Hurricane Polo into western and northwestern Mexico. Local
orography will support lower-level moisture convergence while
upper-level divergence over central Mexico triggers convective
showers across western Mexico and a mix of isolated convective
storms and stratiform rain over the northern Mexican Altiplano.
Throughout the weekend, Hurricane Polo will move northwestward and
is expected to recurve northward in the vicinity of Baja
California. Mid-level and low-level moisture transport associated
with the eastern flank of Polo will support PW enhancement over
the Peninsula and northwestern Mexico, surpassing normal levels
for this time of year by two standard deviations. Daily rainfall
accumulation maxima of 15-35 mm are forecast.

The Bahamas and Caribbean . . .
A cold front will move into the region today and is expected to
become stationary later today into tomorrow over the Bahamas and
Cuba. This system will increase low-level forcing to trigger
scattered showers and thunderstorms over Cuba and the Bahamas
today, with rainfall accumulation totals of 15-25 mm. Upper-level
wind diffluence will develop over central Cuba into the southern
Bahamas and Turks and Caicos tomorrow (Saturday) to enhance upward
motion and stronger storms, leading to rainfall accumulations of
20-35 mm. On Sunday, some showers will occur over the mentioned
region while the stationary front weakens. No significant rainfall
accumulation is forecast over the rest of the Caribbean islands
during the 72-hour period.


Northern South America and Southern Central America . . .
The monsoon trough will extend over southern Central America to
increase low-level moisture convergence in interaction with local
orography today, while strong upper-level divergence will support
deep upward motion across northern Colombia to Costa Rica. A
tropical wave extending over northern Colombia and the regional
orography will interact with lower-level dynamics and significant
moisture influx from the Panama Bight to trigger scattered
thunderstorms mainly over Costa Rica, Colombia, and northern
Ecuador. Daily rainfall accumulation maxima of 30-60 mm are
expected today. A low-level trough and orographic forcing over
Canaima will increase moisture convergence while an upper-level
trough provides support for deep convection aloft. Lower-level
wind confluence over the Amazon Basin will support moderate to
significant moisture confluence, especially over the central
region, where scattered thunderstorms are likely today. On
Saturday, the tropical wave will shift the main area of
disturbances from western Colombia to Costa Rica, where the
stronger moisture convergence will be positioned, while low-level
divergence develops over Panama and western Colombia to limit
precipitation later in the day. Isolated thunderstorms remain
possible over northern Ecuador. Over the central and western
Amazon Basin, low-level moisture convergence will remain strong
with upper-level support, leading to daily totals of 15-35 mm. On
Sunday, low-level favorable dynamics will weaken and turn into
unfavorable conditions over most of the Amazon Basin, while the
area of stronger moisture convergence and upper-level divergence
will shift northwestward into western Colombia and northwestern
Venezuela. Daily rainfall accumulation maxima of 30-60 mm are
expected across this area.

Tropical Waves Initialized at 12 UTC:
TYP SOF  INIT  26/00 26/12 27/00 27/12 28/00 28/12 29/00 29/12
TW  17N   38W  40W  42W   44W   46W  48W   51W  53W   55W
TW  17N   51W  53W  55W   56W   58W  60W   62W  64W   66W
TW  12N   71W  73W  75W   77W   79W  81W   83W  85W   86W
TW  24N   88W  89W  90W   92W   94W  95W   96W  98W   101W


Sanchez-Perez...(WPC)


$$