Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
1237 PM EDT Tue Mar 18 2025

Forecast Bulletin 18 March 2025 at 1640 UTC:

...Mexico...and Central America...

On Tuesday, an upper level trough over the western United States
will extend with its base into extreme northwest Mexico, while to
the south, an upper ridge continues over the region meandering
over most of Mexico and into Central America by Tuesday evening.
Over the west Caribbean a deep upper trough has its base in the
southern portion of the Caribbean Basin and continues propagating
eastward over the Caribbean Basin. In the lower levels, a cold
frontal boundary associated with the upper trough over the
southwest United States extends into west Coahuila, but remains
relatively dry in the region as available moisture is low,
expected to be below 20mm in precipitable water in northern
Mexico. To the south, a weakening frontal boundary associated with
the Caribbean upper trough, is expected over central Honduras,
where precipitable water values of over 40mm are expected to
interact with the terrain as the flow is anticipated from the east
and northeast from the Golfo de Honduras region and into eastern
Nicaragua. On Wednesday, the northern cold front enters Mexico
through northern Veracruz and extends northward along the Sierra
Madre Oriental, where it is expected to remain stationary by
Wednesday evening. Moisture in the region is beginning to
increase, however, no significant precipitation totals are
anticipated as precipitable water values are expected to remain
below 35mm. Isolated showers in northern Veracruz could leave a
trace amount on Wednesday. To the south in Central America, moist
plumes embedded in the easterly trade winds continue the Caribbean
coasts from east Nicaragua through Panama. The greatest impact
from these moist plumes are expected in eastern Nicaragua as
values in precipitable water are expected to exceed 45mm along the
eastern region of the country. On Thursday, the cold front is
expected over from the eastern seaboard of the United States,
trough Florida, and enter the Yucatan Peninsula, where it will
become stationary along central Guatemala, and weaken in the
Sierra Madre Oriental region. An increase in precipitable water is
expected from southern Veracruz through central Guatemala,
suggesting that this moist flow will interact with the terrain and
favor moderate precipitation on Thursday. Conditions in Central
America are expected to remain relatively dry, with the exception
of some advection of moisture in east Nicaragua and east Panama.
Significant amounts of precipitation are not expected.

For Tuesday, expect maxima of 20-45mm from extreme south Belize to
extreme northwest Honduras, and maxima of 15-20mm from the
Honduras Bay Islands into central Honduras. Eastern Nicaragua into
the Providencia and San Andres Islands can expect maxima of
15-25mm. On Wednesday, east Nicaragua can expect maxima of
15-20mm. On Thursday, north Chiapas can expect maxima of 30-60mm,
while south Veracruz can expect maxima of 20-35mm. From Tabasco to
central Guatemala expect maxima of 15-25mm. Generalized maxima of
15-20mm are expected in Nicaragua and east Panama.

...Caribbean Basin...

An upper level trough is expected in the west Caribbean, while the
east Caribbean sees the presence of the Subtropical Ridge that
extends from the Central Atlantic Ocean by Tuesday evening. In the
lower levels, a frontal boundary extends into Hispaniola from the
north and reaches the eastern shores of Honduras. A second frontal
boundary remains stationary over the Central Atlantic and remains
to the east of the Lesser Antilles. A shear line associated with
the front is present in the Caribbean Sea, extending into the ABC
Islands and near the Lake Maracaibo region by Tuesday evening. The
upper trough continues to propagate eastward quickly, weakening
over the Caribbean Basin as the Subtropical Ridge strengthens over
the Central Atlantic from Wednesday into Thursday. This shift will
favor weaker frontal boundaries over the Greater Antilles by
Thursday. A shear line remains over the Caribbean Sea, where its
northeastern tip will meander over the Leeward Islands on
Wednesday and Thursday. Over the next three days, moisture is
expected to remain below 35mm over the Greater Antilles, but the
Lesser Antilles may see values nearing 50mm along the shear line
over the Leeward Islands. However, support from the upper levels
for deep convection remains weak and heavy precipitation is
expected to remain low.

On Tuesday, expect maxima below 10mm in Hispaniola, Puerto Rico,
and the central Lesser Antilles. On Wednesday, similar amounts are
expected in the central Lesser Antilles. On Thursday, expect
maxima of 15mm in the Leeward Islands.

...Tropical South America...

The upper level systems over and near the Tropical region of South
America are expected to strengthen over the next three days,
providing the ventilation in the upper levels over the Amazon
Basin for deep convection as they interact. The Subtropical Ridge
over the Central Atlantic has an axis over the northeast portion
of the continent, while the Bolivian High extends into the western
Amazon Basin with its center just offshore south Peru on Tuesday
evening. In the lower levels, moist plumes propagating along the
ITCZ/NET propagate westward over the Amazon River Basin, providing
the trigger for convection. In west Colombia/Ecuador, moist
onshore flow enters the region and favors moderate precipitation
totals, while having upper diffluence on Tuesday into Wednesday.
By Wednesday evening, the two upper level systems have
strengthened, meandering closer into the continent and their
peripheries interact more over the Central Amazon Basin.
Similarly, the moist onshore flow into west Colombia/Ecuador
encounters divergence from the periphery of the Bolivian High. By
Thursday, the upper level systems continue to meander closer,
enhancing the ventilation over the western portion of the forecast
region. To the east, the presence of the Subtropical Ridge is
favoring subsidence, while in the lower levels, drier air is being
advected into the Guianas along the easterly trade winds.

In terms of precipitation, expect maxima of 30-60mm in
Amazonas-Brasil. While maxima of 20-40mm are expected from west
Colombia to Ecuador, and in the Amazon Delta. Generalized maxima
of 15-35mm are expected in north Colombia into west Venezuela and
in west Para on Tuesday. On Wednesday, expect maxima of 30-60mm in
extreme Northwest Amazon Basin, while maxima of 25-50mm are
expected from southwest Colombia into northwest Ecuador, and the
Central Amazon Basin. Maxima of 20-35mm are expected from the Lake
Maracaibo region into central Colombia, northwest Peru, and the
Amazon Delta region. On Thursday, maxima of 30-60mm are expected
in the West Amazon Basin, and maxima of 25-50mm in west Colombia.
Generalized maxima of 20-40mm are expected in north Colombia, west
Ecuador, and the Amazon Delta region.

For a graphical representation and details of the areas with
forecast rainfall:
https://www.wpc.ncep.noaa.gov/international/crb_day1-3.shtml

Castellanos...(WPC)