Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
1244 PM EDT Wed Mar 18 2026

Forecast Bulletin 17 March 2026 at 1640 UTC:

A mid- to upper-level trough extends from the eastern United
States into Mexico and is anticipated to propagate slowly eastward
throughout the forecast period. At low levels, a frontal boundary,
currently extending from the Bahamas into the Gulf of Honduras,
will continue to be quasi-stationary today. On Thursday, the front
will continue over the Bahamas and Cuba and will start to
propagate eastward, and it is expected to reach the Turks and
Caicos and eastern Cuba by Friday, as a low-level high develops
over the southern United States.The frontal boundary will favor
the development of pre-frontal troughs and will enhance low-level
moisture convergence, increasing precipitation over the Bahamas,
Cuba, Turks and Caicos, and portions of Central America, including
Guatemala, Belize, and northern Honduras, as well as over
Hispaniola toward the end of the forecast period. The mid- to
upper-level trough will further support the development of
thunderstorms and convective activity in the region, increasing
the risk of severe weather. Expect the heaviest rainfall and
thunderstorms over Cuba, the Bahamas, and the Gulf of Honduras
from today through Thursday, with accumulations over Cuba
exceeding 50mm. Precipitation is also expected today through
Thursday over southern Mexico and Guatemala with the presence of a
low-level flow and moisture being advected by northeasterly flow
from the Gulf, with the highest totals ranging between 20-35mm.
Although a lot of the precipitation will likely remain over the
Gulf of Honduras, the northern coast of Honduras could potentially
receive isolated maxima ranging from 20-45mm. Rainfall will then
continue over the Caribbean in eastern Cuba, the Bahamas, Turks
and Caicos, and Hispaniola (mostly over Haiti), and reach northern
Honduras from Thursday through Friday. Totals over Cuba and the
Bahamas will be around 30-60mm, and 20-45mm over Hispaniola. For
northern Honduras, expect precipitation to reach 25-50mm. Early on
Friday, heavy precipitation will continue for western Hispaniola
through Saturday morning, with totals reaching 25-50mm.

For the eastern Caribbean, including the Lesser Antilles and
Puerto Rico, conditions are expected to remain fairly stable with
easterly-southeasterly low-level flow and relatively low PWAT
values prevailing through Friday. Additionally, at mid- to
upper-levels, a ridge will remain over the eastern Caribbean until
the end of the forecast period when the strong mid-to upper-level
trough approaches the region.

In southern Central America, conditions are anticipated to remain
fairly stable, although an increase in precipitation is expected
from Thursday through Friday for the eastern coast of Nicaragua
and for Costa Rica, and from Friday through Saturday for Costa
Rica and Panama, as strong northerly low-level flow increases
moisture advection in the region. Low-level cyclonic flow will
also contribute to the development of rainfall activity in the
region. The highest totals are expected from Friday through
Saturday for Costa Rica and Panama, with accumulations around
20-45mm.

In northern South America, most of the precipitation today through
Thursday is expected over the Central and Eastern Amazon Basin,
where moisture is being advected and low-level winds converge.
Additionally, upper-level diffusion from the periphery of the
Bolivian High to its south and ridging to the northeast will
support the development of convection and heavy thunderstorms in
the area. The highest accumulations are expected to be around
35-70mm, today through Thursday morning. Another area of interest
is the Amazon Delta region, as a plume of moisture over the
Atlantic and a low-level trough approaching the region continue
advecting moisture and promoting instability. Over Colombia and
Ecuador, expect light to moderate rainfall as most of the moisture
in the region will remain over the Amazon basin, but upper-level
divergence and low-level flow convergence will cause showers
particularly over Colombia, leading to accumulations ranging from
20-35mm. After Thursday, a drying trend is expected for the
western part of tropical South America, but heavy precipitation
will continue over the Eastern Amazon and Amazon Delta regions due
to moisture advection from the Atlantic, the presence of a
low-level trough, and low-level winds converging in the area.
Heavy precipitation reaching 50-100mm is expected for the eastern
Amazon from Thursday through Friday. Over the Amazon Delta, with
the low-level trough in the region, accumulations are expected to
be around 30-60mm. An additional 50-100mm is expected for the
eastern part of tropical South America from Friday through
Saturday.

Rivera-Torres...(WPC)