Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
315 PM EDT Tue Sep 15 2026

Forecast Bulletin 14 September 2026 at 1900 UTC:

Mexico:

Over much of the region, a progressive pattern of retrograding
upper
air systems are moving over Mexico in the next three days, bringing
precipitation over the country, varying in intensity over the
different regions. On Tuesday, the northern portion of the country
can
expect a ridge axis extending from the southern United States
alongside a Tropical Upper Tropospheric Trough (TUTT) from
Texas-United States into northeast Mexico. A secondary ridge axis
remains over much of the central portion of Mexico, while a
secondary
TUTT reaches southwest Mexico from the east Pacific Ocean. To the
east, the Yucatan Peninsula remains at the periphery of a wide TUTT
that centers over the Greater Antilles of the Caribbean. In the
mid-levels a more ridge dominant pattern remains consistent
throughout
the region. Mexico is in the periphery of the ridge, where some
shortwave troughs could travel along the region to enhance
instability
on Tuesday and throughout the next three days. Moisture over the
western sector of Mexico will enhance the chance for showers during
the day, while onshore flow along the Sierra Madre Occidental
enhances
the orographic lift over the region. Expect maxima to remain below
25mm in western Mexico, while the eastern portions of the country
could see totals below 15mm, as dry air continues to enter from the
north Caribbean. By Wednesday, the pattern begins to shift, as a
TUTT
over the Caribbean retrogrades into the Yucatan, favoring the
entry of
moisture along the Gulf coast of Mexico and into the Yucatan
Peninsula. Over the western sector of the country, drier conditions
are expected with the enhancement of the mid to upper level ridge
over
the region, fortifying the interaction with the retrograding TUTT
to
its east. Expect light to moderate precipitation along the Sierra
Madre Oriental and scattered rainfall in the southwest and Yucatan
Peninsula.

Central America:

On Tuesday, the base of a large TUTT is located over the southwest
Caribbean and from east Nicaragua through Panama, where mid to low
level troughing is enhanced with high amounts of precipitable
water.
The areas with the highest levels of available moisture are Panama
and
Costa Rica, where a trough is propagating into the central Panama
region throughout the day. With support of the Caribbean Low Level
Jet
(CLLJ), enhanced moist onshore flow will favor heavy precipitation
from Limon-Costa Rica through the northeast sector of Panama on
Tuesday. To the north, expect moisture to begin entering the
Mosquito
Coast in Honduras and making its way further inland, favoring light
showers on Tuesday. On Wednesday, moisture continues to transport
ahead of the CLLJ, proceeding to interact with the complex terrain
from east Honduras through Panama. The TUTT continues retrograding
into the region, while interacting with a ridge to its east,
enhancing
upper level support due to diffluence from their interaction.
Expect
an increase in precipitation totals along the Mosquito Coasts of
Honduras and Nicaragua. On Thursday, the upper ridge over the
Caribbean continues to meander into Central America, while the TUTT
continues retrograding westward into the Pacific and Mexico.
Subsidence due to the ridge aloft may inhibit the growth of
convection
over the region, while available moisture remains along the
Caribbean
coasts of Honduras, Nicaragua, and into Costa Rica and Panama.
Expect
a general decrease in total daily precipitation over Central
America
on Thursday, with isolated locally moderate precipitation.

Caribbean:

Much of the central Caribbean is seeing the presence of a
retrograding
TUTT that is enhancing instability over the region on Tuesday.
Troughs induced by the TUTT and a tropical wave moving over the
Caribbean Sea, are favoring precipitation over Hispaniola, with
precipitable water values exceeding 55mm, as they interact with the
TUTT aloft. Expect moderate precipitation with isolated locally
heavier totals in higher elevations. On Wednesday, a second
tropical
wave enters the east Caribbean, providing precipitation for the
Lesser
Antilles and into Puerto Rico/VI. This wave will bring with it
moisture values exceeding 60mm, and favoring moderate to locally
heavy
precipitation over much of the Lesser Antilles on Thursday.
Disorganized mid to upper level short wave troughs along the
periphery
of the ridge axis extending over the Central Atlantic will provide
divergent conditions for the wave, fueling convection. By Thursday,
these conditions will meander to the west and impact Puerto Rico
and
the Dominican Republic. The regions could expect moderate to
isolated
locally heavier precipitation.

South America:

The regions of enhanced potential for moisture is expected over
northwestern South America as the warm sea surface temperatures and
fueling the development of convection are the Panamanian trough and
monsoon trough enhanced on Tuesday. With the entry of tropical
waves
expected over the next several days, this enhanced cyclonic
circulation will favor westerly onshore flow into west Colombia and
west Ecuador and with the amount of moisture in the region, expect
moisture convergence along the higher terrain. Expect daily
moderate
to locally heavy precipitation from west Colombia through northwest
Ecuador. To the east, the Guianas and the Amazon Basin could expect
generally dry conditions as the ridge enhances subsidence over the
region over the next three days.




Tropical Waves Initialized at 12 UTC:
SOF  INIT 16/00 16/12 17/00 17/12 18/00 18/12 19/00 19/12

TW  20N   56W  59W  62W  65W  68W  71W  74W  77W  78W
TW  12N   69W  72W  74W  76W  79W  81W  84W  87W  90W  
TW  17N   105W  107W  109W  110W  112W  113W  115W  117W Exits



Castellanos...(WPC)