Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
308 PM EDT Tue May 12 2026

Forecast Bulletin 12 May 2026 at 1900 UTC:

Over the next three days, portions of Tropical South America and
western Mexico are expected to receive significant rainfall. Today
being the rainiest day across the region, while a drying trend is
expected with each passing days. The shower and thunderstorm
activity across Tropical South America will go from numerous
today, to isolated or scattered by Thursday. In general, the
Caribbean region will observe isolated and shallow convection, as
a mid and upper level high pressure continues to dominate the
local area, causing subsidence. That being said, there is a
frontal boundary moving south and into the northern Bahamas that
could cause periods of thunderstorms over the area.

Mexico and Central America:

Onshore low-level flow will move into western Mexico today and
Wednesday, causing orographic lifting across the area, developing
showers and thunderstorms. Onshore flow will also affect portions
of Veracruz today, which, when combined with diurnal heating, will
promote some shower and thunderstorm activity today. The low-level
onshore flow will not be as persistent with each passing day this
week. Therefore, the rainfall amounts over the area are forecast
to have max values of 35mm or less. Further south across Central
America, the mid and upper level high pressure will keep a
relatively stable atmosphere, but the moisture near the Monsoon
Trof, combined with the local terrain, will cause some showers and
thunderstorms each day, though the daily max rainfall will be near
25 to 45mm, mainly over Costa Rica and Panama. Elsewhere in
Central America, generally isolated and shallow convection is
expected.


Tropical South America:

Heavy precipitation is expected today over Tropical South America,
in particular, portions of northern Brasil into Venezuela. The Max
rainfall totals forecast today could be as high as 80mm within
that region, though the latest model guidance had some isolated
areas with higher amounts. Some portions of western Colombia could
observe up to 45mm. Elsewhere, rainfall could be in the 15 to 35mm
range. Wednesday and Thursday is expected to have slightly lower
amounts of rain, with the heavy thunderstorm activity becoming
more scattered on Wednesday, then isolated on Thursday. In terms
of total rainfall, significant amounts can still be expected on
Wednesday, but the overall coverage is expected to decrease with
each passing day.

The Bahamas and Caribbean:

The mid and upper level high pressure will dominate and keep
convection relatively shallow over the area. Daily rainfall maxima
will be generally in the order of up to 15mm, though some isolated
areas could observe up to 35mm. These isolated higher amounts of
rain would be due to the combination of the available moisture and
local effects of each island. The mid-level high pressure has a
high positive anomaly, which, according to the latest guidance
will prevail until this weekend.



Alamo...(WPC)