Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
202 PM EDT Fri Mar 13 2026

Forecast Bulletin 13 March 2026 at 1805 UTC:

Over the next few days, the forecast region will remain under a
divergent upper level pattern due to the propagation of the
Madden-Julian Oscillation, as suggested by model guidance.
Although uncertainty in its propagation and strength still
remains, the potential for the divergence aloft over the next
three days will provide ventilation for areas that can expect deep
convection and favor locally heavy precipitation.

In Mexico and northern Central America, the remnants of a frontal
boundary are expected over the Yucatan Peninsula by Friday
evening, where expect enhanced moisture convergence over the
Yucatan and into central Guatemala and Belize, particularly from
Friday afternoon and into the early hours of Saturday. In the mid
to upper levels, the base of a weak trough is situated over the
Bay of Campeche, while it interacts with a dominating mid level
ridge that extends over most of southern Mexico, north Central
America, and into the western Caribbean. This will favor weak
divergence in the mid to upper levels, assisting the convection
over the Yucatan and into Guatemala and Belize on Friday into
Saturday, and a potential for light to moderate precipitation. On
Saturday, a weak shortwave trough enters northeast Mexico, while
interacting with the more zonal wind flow, enhancing speed
divergence over the southern Sierra Madre Oriental region and into
the Yucatan, Guatemala, and Belize. As moist plumes continue to
propagate into the region along the trade winds, moisture
convergence is expected over the region and moderate precipitation
totals are likely on Saturday. On Sunday, a potent upper level
trough over the United States is favoring the development of a
strong cold front propagating over the southern United States and
entering northeast Mexico by early Sunday afternoon. Prefrontal
troughing over Tamaulipas will favor light precipitation on Sunday
into Monday. Over Guatemala and El Salvador, a shift of
northwesterly winds along the coast in the lower levels will favor
moist onshore flow into the Altiplano Central and Bocacosta
regions, as well as into El Salvador, while generally eastward
flow enters the region from the Caribbean, will favor moisture
convergence and orographic lift over the region. Expect light to
moderate precipitation totals on Sunday.

In the Caribbean, the presence of the weakening frontal boundary
is expected over the northern Bahamas, while weak moist plumes
reach the Greater Antilles by Friday evening. As a weak upper
level jet streak is present at the base of the weakening wide
upper level trough over the north Caribbean, expect this region to
see some enhancement in convection due to the upper level support.
However, due to the decreasing amounts of available moisture
expect light precipitation on Friday. On Saturday, in the mid
levels, a series of shortwave troughs are expected to propagate
over the southern United States and into the Bahamas as the mid
level trough over the southern United States interacts with the
expanding mid level ridge over the Caribbean. The periphery of the
mid-level ridge is seeing dry conditions that will assist with the
instability of the region, favoring marginal to slight chances of
severe weather on Saturday over the north Caribbean and the
Bahamas. On Sunday, a mid to upper level shortwave trough enters
the region, favoring divergent conditions and ventilation for deep
convection into the north Caribbean and the Bahamas. This enhanced
unstable state will favor a slight risk of severe weather in Cuba
and the Bahamas.

In the tropical South America region, a dryier trend is expected
to emerge over the next three days, with the advection of dry air
from the Central Atlantic especially from late Saturday into early
Monday. On Friday, moist plumes continue to enter the continent
from the east and continue to propagate over the east and central
Amazon Basin. In the upper levels, there is generalized ridging
that extends from the ridge over the Central Atlantic into north
South America that has weak interaction with ridging further south
into central South America, allowing for weak upper level
diffluence over the east and central Amazon basin. Expect to see
deep convection continue to develop on Friday in the afternoon
hours. The Bolivian High is centered over the Pacific Ocean, just
west of south Peru, as it extends over southern Ecuador and north
Peru on Friday. This will provide speed diverge aloft for deep
convection over the region and expect moderate precipitation
totals on Friday. On Saturday, the Bolivian High meanders inland,
beginning to reach into the central Amazon Basin by Saturday
evening. The divergence aloft over Ecuador and north Peru remains
on Saturday, however, expect a decrease in available moisture
along the western coasts as drier air from the south along the
Peru coast beings to enter the region. This will favor a decrease
in precipitation totals for Saturday. On Sunday, this drying trend
is expected to continue although the divergence aloft is present,
meaning light precipiation is expected in western Ecuador and
northwest Peru. Over the Amazon, dry air is being advected from
the Central Atlantic, but the moisture remains Ecuador and north
Peru, where they will also experience the diffluence from the
Bolivian High, favoring moderate to heavy precipitation on Sunday.
Similarly, the eastern Amazon can expect to see divergent
conditions aloft which will enhance the deep convection in the
region. Expect moderate to heavy precipitation totals on Sunday.

Castellanos...(WPC)