Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD


Forecast Bulletin 28 August 2026 at 1540 UTC:

Mexico and northern Central America...
Conditions over Mexico are expected to remain similar on Friday
and into the weekend. A potent mid to upper level ridge meanders
over the southern United States, extending into central Mexico and
remains in a similar location over the next three days. From the
east, a mid to upper level trough, although weakening, retrogrades
from the west Caribbean into the Yucatan Peninsula, interacting
with the periphery of the ridge aloft. This will weaken the extent
of the ridge over the central and southwestern portions of Mexico,
enhancing divergence aloft primarily in the southwest Mexico
region. In the lower levels, tropical waves are propagating along
the monsoon trough and have a northward extent from Jalisco
through Oaxaca, favoring moist onshore flow along the Sierra Madre
del Sur and along the continental coast of the Gulf of California
with moisture advecting along the coast. Expect light to moderate
daily precipitation totals from west through southwest Mexico.
Central America continues to see low amounts of available moisture
even with the passing of tropical waves entering the area. As the
upper trough over the west Caribbean retrogrades into the
continent and weakens, it is allowing for the the easterly trades
along the periphery of the potent central Atlantic high pressure
system to dominate the entry of dry conditions in the mid levels
and amplify trade wind inversions that will limit the development
of deep convective systems. Trace to light amounts of
precipitation are expected daily from Guatemala, through Belize,
Honduras, El Salvador, and northern Nicaragua.

Caribbean...
An upper-level low located over the western Caribbean is expected
to retrogress westward, making way for a building anticyclonic
circulation to become the dominant synoptic feature across the
Caribbean. An upper- and mid-level high-pressure system, with
ridging extending into the eastern Caribbean, is interacting with
a tropical wave currently located near the Leeward Islands.
Precipitation amounts of approximately 1 to 10mm are expected. The
advection of dry air into the Caribbean, together with increasing
subsidence associated with the mid-level ridge, is resulting in
atmospheric conditions that are generally less conducive to the
development of deep convection. The strengthening mid-level ridge
is expected to maintain a stable environment across much of the
region, limiting the vertical development of convection despite
the presence of the tropical wave or enhanced convection. By
Saturday, the ridge is forecast to extend farther into the central
Caribbean, while the tropical wave continues to move westward
across the Puerto Rico and ABC Islands region. Limited moisture
availability and increasingly stable atmospheric conditions are
expected to inhibit significant deep convection across these
areas. Precipitation amounts of approximately 1 to 5mm are
expected, with trace amounts elsewhere. The moderate to strong
Caribbean Low-Level Jet is expected to accelerate the westward
progression of the tropical wave into the western Caribbean. In
combination with the strengthening mid-level ridge, the low-level
jet will enhance subsidence and maintain a relatively dry and
stable environment, limiting significant cloud development and
deep convection. By Sunday, the remnants of Tropical Storm Dolly
are expected to reach the Leeward Islands. A weak upper-level
trough accompanying the system is expected to enhance divergence
aloft, providing additional upper-level support for the
development of deeper convection across the northeastern
Caribbean. The remnants of Dolly are also expected to temporarily
weaken the mid-level ridge, resulting in a less stable atmospheric
environment and allowing deeper convection to develop across much
of the Lesser Antilles. Consequently, rainfall totals of
approximately 25 to 50mm are possible across the Leeward Islands,
while 10 to 20mm are expected across the Windward Islands. Locally
higher amounts are possible, with rainfall totals varying from
island to island depending on orographic enhancement and the
persistence of showers and thunderstorms.

South Central America and northern South America...
This region can expect to see the propagation of multiple tropical
waves throughout the forecast period. On Friday, the upper level
trough retrogrades westward, with the base over Costa Rica and
Panama, where it interacts with the periphery of a ridge over the
east Pacific. The diffluence in the region will ventilate deep
convection associated with a tropical wave entering Panama by
Friday evening. Enhanced cyclonic circulation in the monsoon
trough, will favor moist onshore flow into the Caribbean coast of
Costa Rica, where expect heavy precipitation on Friday. To the
east, dry air advection will limit precipitation throughout the
day. Expect trace to light precipitation from Venezuela through
the Guianas on Friday. On Saturday, the tropical wave enters Costa
Rica, continuing the pattern of moist onshore flow. However, the
cyclonic circulation in the lower levels is favoring moist onshore
from the west into the Pacific coasts of Costa Rica and Panama, as
well as west Colombia, favoring an enhanced risk of heavy
precipitation in the region. To the east, continued drying trend
will favor trace amounts throughout much of the eastern sector of
the forecast region. By Sunday, the tropical wave continues west
into the East Pacific, however westerly moist onshore flow is
expected to continue into western Colombia, the Choco region.
Orographic lift can enhance the converging moisture and favor deep
convection throughout the day.

Tropical Waves Initialized at 12 UTC:
TYP SOF INIT 29/00 29/12 30/00 30/12 31/00 31/12 01/00 01/12
TW 15N  26W 29W 32W 35W  38W 41W 44W  46W 48W
TW 19N  60W 64W 69W 73W  77W 80W 83W  87W 90W
TW 16N  74W 77W 80W 84W  87W 90W 94W  97W 101W
TW 18N  93W 97W 100W 103W 105W 107W 108W 109W 110W
TW 17N  101W 103W 106W ABS

Luciano...(MDC)
Castellanos...(WPC)