Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
229 PM EDT Thu Apr 30 2026

Forecast Bulletin 30 April 2026 at 1830 UTC:

Southern Central America and Tropical South America...
A moist propagating wave is located over the Gulf of Panama on
Thursday morning with precipitable water levels reaching 70mm just
north of Panama. Its slow progression over the region is in part
due to the presence of a mid to upper level trough over the
western Caribbean that enters the east Pacific on Thursday. Expect
the regions of eastern Costa Rica, northern Panama, and the west
coast of Colombia to see moist onshore flow favor deep convection
and heavy precipitation. In the southern portion of the area of
circulation, it will coincide with the confluence of winds from
the west in the lower levels that will enter the western coast of
southern Colombia and provide additional fuel to the convection in
the region. Over the Amazon Basin, other propagating troughs move
over the region with moisture associated with them, reaching over
70mm on Thursday. Expect diurnal thunderstorms and showers which
may produce moderate to locally heavy precipitation totals over
much of the Amazon Basin. On Friday, the propagating trough
meanders over central Panama by the evening hours, with a wide
area of circulation reaching southeastern Nicaragua and extending
south into western central Colombia. Enhanced levels of moisture
continue throughout the circulation, continuing to favor heavy
precipitation over eastern Costa Rica, the northern coast of
Panama and into the central portions of west Colombia. At this
time, the amount of deep convection that is expected from this low
level trough has ample latent heat release to help generate
ridging in the upper levels and ample outflow in the upper levels.
Over the Amazon River Basin, a similar pattern is present in terms
of localized heavy precipitation over the region. In the upper
levels the Subtropical High is reorganizing towards eastern
Brasil, favoring areas of diffluence in its periphery, expected
over the Amazon Delta and the eastern Amazon Basin, due to the
interaction with another ridge developing just north of the
Guianas by Friday evening into Saturday. By Sunday, the
propagating trough over southern Central America begins to
increase in speed and is expected along the Costa Rica/Panama
border, with a northern extent into central Nicaragua, and
favoring moist onshore flow into north and central Colombia. These
regions can continue to expect heavy total precipitation, with
some regions exceeding 70mm in accumulated rainfall for Saturday.

Caribbean and The Bahamas...
In the upper levels, a weakening trough extends over much of the
western Caribbean, with a broader trough extending just north of
the Greater Antilles and into the central Atlantic Ocean. This
broader trough is favoring the progressive passage of a frontal
boundary that is expected over the central Atlantic by the evening
on Thursday, with its western portion of the front  weakening over
the Greater Antilles. Due to the low amounts of available
moisture, light to moderate precipitation totals are expected in
Hispaniola, with some locally heavier totals on Thursday. On
Friday, the front is expected to transition to remnants and
meander over the Greater Antilles as low level troughs. These
remnants continue with moderate levels of moisture that will favor
light to moderate precipitation over Hispaniola and in Puerto
Rico. The rest of the Greater Antilles and the Lesser Antilles can
expect drier conditions with diurnal showers producing trace
amounts to light precipitation totals on Friday. By Saturday, a
new broad upper trough extends from the southern United States and
reaches the northern Bahamas and west Cuba overnight into early
Sunday morning. With it, a cold front advances and favors
precipitation activity over the northern portion of the islands
with a slight chance of severe weather overnight.

Mexico and Northern Central America...
The dry pattern that has been persistent will begin to shift over
the next three days. On Thursday, a potent shortwave trough enters
southern California and reaches the Baja California Peninsula
throughout the day, favoring troughing in the lower levels, and
advection of moisture from the tropics in the mid levels,
increasing the amount of available moisture into northwest Mexico.
A frontal boundary over the southern United States is enhanced as
this shortwave trough enters the central regions of Mexico and
Southwest United States, favoring moisture convergence in the
lower levels, including northern Mexico, where expect a chance of
severe weather, with moderate precipitation totals. With the
lowering of pressures in the southern United States, expect
southerly flow along the eastern Mexico region, along the Sierra
Madre Oriental, to bring moisture from the south and interact with
the mountain range, favoring light to moderate precipitation from
the central Eje Volcanico Transversal and northward into Coahuila
and Nuevo Leon on Thursday. By Friday, the upper level shortwave
trough is reinforced by broader upper trough from the north,
enhancing the frontal boundary and helping it advance as a cold
front over the southern United States and into Tamaulipas, the
northern Sierra Madre Oriental, and the northern Mexican Plateau.
These regions can expect light to moderate precipitation with a
risk of severe weather. By Saturday, the cold front makes its way
into central Veracruz and along the Sierra Madre Oriental, also
favoring the presence of prefrontal troughing reaching into
southern Veracruz, extending into northern Oaxaca, Tabasco, and
northern Chiapas, where increased moisture convergences along the
mountain range is expected. Expect moderate to heavy
precipitation, with a possibility for locally higher amounts.
Increased amounts of available moisture are also reaching
Guatemala, and the higher elevations of Honduras and El Salvador.
Expect light to moderate total precipitation on Saturday.

Castellanos...(WPC)