Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
117 PM EDT Mon Mar 17 2025

Forecast Bulletin 17 March 2025 at 1715 UTC:

In the larger scale, the region is under a convergent phase of the
Madden-Julian Oscillation (MJO) which favor a generalized
suppression of precipitation. This pattern is expected for the
forecast period. Another oscillation of interest is the North
Atlantic Oscillation (NAO), which currently is in a negative
phase, favoring frontal passages into the Caribbean region, which
is expected over the next three days. Overall, the region may
expect mostly drier conditions with insignificant to localized
moderate amounts of precipitation. The exception may be north
South America, where there is more available moisture and the
presence of diffluence in the upper levels, favoring deep
convection in the next three days.

...Mexico...Central America..and the Caribbean Basin...

An upper level trough extends into the western Caribbean, where a
frontal boundary is expected from the eastern seaboard of the
United States into The Bahamas, Cuba, and enters Belize, becoming
stationary in central Guatemala and portions of Chiapas by Monday
evening. The northeasterly flow will favor onshore into Belize,
Central Guatemala, and portions of west Honduras, where it will
interact with the terrain favoring moderate precipitation. To the
west of this system, a ridging pattern is becoming more defined in
the upper levels over Mexico and southern Central America as a
ridge axis associated with the Subtropical Ridge over the
Caribbean Sea extends into the region. To the east, a Tropical
Upper Tropospheric Trough is located in the Central Atlantic,
northeast of Puerto Rico/VI. A frontal boundary and trough in the
lower levels associated with this system have regenerated from
remnants of a previous frontal boundary. The boundary is expected
to remain to the east of the Leeward Islands, yet a trough extends
into the north Leeward Islands and into Puerto Rico, while a
frontal shear line is expected over the central Lesser Antilles on
Monday. precipitation is expected to remain in the lower range
over the region. Into Tuesday, the western most frontal boundary
continues to propagate south and eastward into the Central
Atlantic, central Hispaniola, entering east Honduras/Nicaragua,
and weakening over north Central America. The secondary frontal
boundary is expected to also weaken over the Central Atlantic and
over the Lesser Antilles yet the shear line remains present
meandering southwest into the ABC Islands and northwest Venezuela
by Tuesday evening. On Wednesday, the main frontal boundary has
now progressed over the Greater Antilles, becoming stationary and
weakening over Jamaica and the Cayman Islands. From the remnants
of the previous shear line, a prefrontal shear line associated
with this frontal boundary is located just west of the Leeward
Islands and enters the ABC Islands by Wednesday evening. Localized
showers are expected in the region with this system. To the west,
a new frontal boundary has entered Mexico and expected from the
southeastern United States, and entering into Tamaulipas, Nuevo
Leon, and along Coahuila. A prefrontal trough extends into
northern Veracruz, where showers are expected as moisture
increases in the region.  The upper level ridge is expected to
favor dry conditions over portions of Mexico, Central America, and
most of the Caribbean Basin on Monday and into the rest of the
week. In addition, the amount of available moisture in the region
remains low and scattered over isolated areas associated with the
front and moisture plumes in the trade winds.
Moist plumes are expected along the easterly trade winds which
will bring some moisture into eastern Nicaragua over the next
three days.

In terms of precipitation, on Monday expect maxima of 35-70mm in
central Guatemala, and maxima of 15-30mm from Chiapas, north
Guatemala, and north Belize. The central Bahamas can expect maxima
of 15-25mm with a marginal risk of severe weather as the upper
trough propagates over the region. Expect similar amounts in Cuba.
On Tuesday, the Golfo de Honduras region can expect maxima of
20-45mm, while east Nicaragua can expect maxima of 15-25mm. The
Greater Antilles, central Lesser Antilles and the ABC Islands can
expect maxima of 10mm. On Wednesday, expect generalized maxima of
15-20mm in north Veracruz, east Nicaragua, and the Lesser
Antilles. Maxima of 10mm are expected in the ABC Islands.

...Tropical South America...

In the northern region of South America, the periphery of the
Bolivian High is interacting with the periphery of the subtropical
ridge over the Central Atlantic, northeast of South America, as
well as with the base of the upper level trough that is
propagating over the southern Caribbean Basin over the next three
days. These regions will have enhanced upper level diffluence for
ventilation of convection. In the lower levels of the atmosphere,
moist troughs are propagating over north South America, favoring
convection primarily over the Amazon River Basin over the next
three days. To the west, low-level moist onshore flow from
generally the northwest direction will favor convection along west
Colombia and into Ecuador, where expect heavy precipitation on
Monday. By Tuesday, this flow shifts to a generally north
direction, decreasing the chances for heavy precipitation in the
region. On Wednesday, west Ecuador can expect some favorable
northwestward onshore and ventilation from the upper levels, where
expect moderate amounts of precipitation on Wednesday.

In terms of precipitation, on Monday, expect maxima of 35-70mm in
west Colombia, maxima of 30-60mm in west Ecuador, while maxima of
25-50mm are expected in northwest and southwest Colombia, as well
as in the central Amazon Basin. Maxima of 20-35mm are expected in
the Eastern Amazon Basin and the Amazon Delta. On Tuesday, expect
maxima of 25-50mm from west Para to east Amazonas-Brasil, as well
as the Lake Maracaibo region. Maxima of 20-45mm in eastern
Colombia, while generalized maxima of 15-35mm are expected in west
Colombia, west Ecuador and Para/Amapa-Brasil. On Wednesday, expect
maxima of 25-50mm in east-central Amazon Basin and east Ecuador,
while maxima of 20-35mm are expected in the Lake Maracaibo region,
the western Amazon Basin, and the Amazon Delta. Maxima of 20-40mm
are expected in western Ecuador. Elsewhere in northern South
America expect isolated to scattered thundershowers with maxima
below 25mm.

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)