340
FXCA20 KWBC 131801
PMDCA

Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
201 PM EDT Mon Jul 13 2026

Forecast Bulletin 13 July 2026 at 1805 UTC:

Mexico...
In the greater scale, the divergent phase of the Madden-Julian
Oscillation is beginning to enter the region, expanding from the
Eastern Pacific Ocean. The presence of the enhanced upper level
divergence is likely to provide ventilation for deep condition
from synoptic systems in the country. These conditions are
forecast to continue for the rest of the week, in accordance with
the long-term model guidance available. On Monday, over the
western sector of the country, a negatively tilted upper level
trough extends over the Baja California Peninsula, amplifying the
convection in the northwest portion of Mexico, where the advection
of moisture associated with the passing of a tropical wave to the
south will favor moderate to heavy precipitation on Monday along
the foothills of the southern Sierra Madre Occidental and western
Eje Volcanico Transversal regions. Along the northern Mexican
Altiplano, low level troughing produced by a developing closed low
over the Lower Mississippi River Basin, enhanced by the
southeasterly moist flow along the eastern coast of the country,
favoring moderate precipitation, with potential for locally heavy
totals from Monday into Tuesday. In the southern regions of
Mexico, expect light to moderate rainfall totals while a tropical
wave enters along Chiapas from late Monday into early Tuesday
morning. On Tuesday, the upper level cutoff low remains centered
over the southern Baja California Peninsula, enhancing local
diffluence over the northern Sierra Madre Occidental region, where
expect heavy precipitation on Tuesday. Moisture convergence
extends from the southern Pacific coast, favoring moisture
convergence from the Sierra Madre del Sur into western Mexico.
Moderate precipitation totals are expected along from Jalisco
through Michoacan. Over the Yucatan, a Tropical Upper Tropospheric
Trough (TUTT) retrogrades from the west Caribbean, with its base
extending from Chiapas into northern Central America, favoring
convection along the upper extent of a tropical wave entering
southern Mexico. By Wednesday, the upper level cutoff low meanders
west over the East Pacific and the southern Baja California
Peninsula, interacting with a developing ridge along the Pacific
coast of Mexico. Enhanced divergence due to this interaction will
favor moderate to heavy precipitation over the northern Sierra
Madre Oriental. Along the southern Mexico region, the tropical
wave propagating there will favor light precipitation due to the
decrease in available moisture. Much of the moisture remains over
the Eastern Pacific, as dry air advection from the Caribbean
reaches Mexico. Of note, the National Hurricane Center is watching
two regions of potential tropical cyclone development associated
with the two tropical waves aforementioned. Please see information
from the NHC (https://www.nhc.noaa.gov/) for the most up to date
information about these areas of interest.

Central America...
Over the western Caribbean, the base of a retrograding TUTT
meanders over Central America, with the divergent side remaining
over much of the Caribbean coasts of the region on Monday. This
region of enhanced divergence is coupled with the propagation of a
tropical wave that is entering with amplified moisture, favoring
moisture convergence in the Caribbean coasts from Honduras through
Costa Rica. Expect maxima to exceed 30-60mm, with locally heavy
precipitation. Similarly, the Gulf of Honduras region can expect
enhanced moisture convergence due to the channeled moisture
advection into Belize and Guatemala, favoring moderate
precipitation values on Monday. The rest of Central America can
expect light to locally moderate precipitation totals due to the
moisture present in the region. On Tuesday, the first tropical
wave quickly propagates west, while another wave is propagated
quickly as the Caribbean Low Level Jet favors fast propagation of
waves. As this feature approaches the Caribbean coastal regions of
Central America, moisture is expected to converge along this
region, favoring maxima of 35-70mm, with locally higher
precipitation totals possible. This also means that increased
moisture continues over the Continental Divide, favored by the
divergence of the TUTT, which continues to retrograde over Central
America, favoring moderate precipitation on Tuesday in northern
Central America. By Wednesday, the tropical wave over the west
Caribbean is expected to enter the Gulf of Honduras and Gulf of
Fonseca regions by the evening hours, advecting more moisture into
the region. Expect heavy precipitation totals in Belize and
central Guatemala, as well as in Costa Rica, while east Honduras
and Nicaragua can expect maxima of 40-80mm, with potential for
heavier precipitation totals.

The Bahamas and Caribbean...
On Monday, the majority of the region conditions to experience a
dry pattern amplified by the Saharan Air Layer from the east. Much
of the islands in the region can expect trace amounts, with a few
regions expecting maxima to reach 10-15mm. On Monday, Cuba and
Hispaniola can expect light precipitation due to the propagation
of tropical waves over the region, while Jamaica can expect a
moist plume to enter and interact with the terrain and favor trace
to light precipitation. On Tuesday, generally dry conditions
continue with the potential for trace amounts with the advection
of moist plumes along the overall dry air advection along the
easterly trade winds. By Wednesday, the TUTT over Cuba will
interact with the moisture of the tropical wave entering the
region and favor light precipitation with a marginal risk of
severe weather in the central and eastern portions of the island.
Over the Leeward Islands, the entry of a new tropical wave will
bring some moisture and precipitation totals of under 10mm.

Northern South America...
The region of tropical South America is also expected to see a dry
trend over the next several days as dry air is being advected
along the trade winds from the Central Atlantic as well as from
the south due to a potent ridge extending from east of Brasil in
the Atlantic. Most of the moisture is expected in northwest South
America, in association with the propagating tropical waves over
the Caribbean. As this moisture is advected westward, this moist
flow will undergo orographic lift along the Andes Mountains.
Expect moderate precipitation from the Maracaibo region and into
central Venezuela with the passing of a tropical wave, while the
rest of the northern portion of South America is expected to see
trace to light precipitation. By Tuesday, the tropical wave enters
northwest Venezuela into northeast Colombia, where expect moderate
precipitation into central Colombia. On Wednesday, the tropical
wave enters eastern Panama, favoring moderate precipitation totals
along western Colombia, while residual moisture remains over
central Colombia and similar precipitation totals are forecast. To
the east, from northeast Venezuela into northern Guyana can expect
a tropical wave to favor light precipitation as it interacts with
a generally dry environment due to the Saharan Air Layer.

Tropical Waves Initialized at 12 UTC:
SOF INIT 14/00 14/12 15/00 15/12 16/00 16/12 17/00 17/12
20N 27W  30W 33W 37W 40W 44W 47W 50W 53W
18N 40W  44W 48W 52W 56W 60W 63W 66W 69W
16N 61W  65W 68W 72W 75W 78W 81W 84W 87W
20N 70W  74W 78W 81W 84W 87W 90W 93W 96W
18N 80W  84W 88W 91W 94W 97W 100W 104W 108W
20N 100W 104W 107W 110W 113W 115W 117W EXITS ---

Castellanos...(WPC)


$$