Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
313 PM EDT Mon May 18 2026

Forecast Bulletin 18 May 2026 at 1915 UTC:

Across Mexico...

A dynamic mid-to-upper level atmospheric pattern will persist
across northeast Mexico over the next three days. On Monday, an
upper-level jet streak will drive the development of a mid-level
shortwave trough in the afternoon. At the same time, southerly low
level winds will be strong and it will support the transport of
moist tropical air into northeast Mexico and the Central Plains of
the United States. Expect enhanced moisture convergence in
Tamaulipas and northern Veracruz with this pattern, where moderate
rainfall accumulations are anticipated. Thereafter, upper-level
divergence will continue to dominate across the region,
accompanied by a series of developing mid-level shortwave troughs.
However, precipitable water values will decrease across the Gulf
states on Tuesday and Wednesday. Moisture convergence will peak
across Tamaulipas and Nuevo Leon on Wednesday, driven by a brief
resurgence of easterly and southeasterly low level winds. Thus,
expect moderate rainfall accumulations for Wednesday in this
region.

In central Mexico, diurnal showers and thunderstorms will prevail
over the next three days. The most intense precipitation
accumulations are expected on Tuesday and Wednesday, when a
mid-to-upper level trough will increase upper-level divergence and
vertical lift. While there will be light accumulations due to
orographic effects on Monday, moderate rainfall is likely across
the broader region on Tuesday and Wednesday.

Across the Bahamas, Greater Antilles, and Lesser Antilles...

A potent, negatively tilted mid-to-upper level trough currently
has an axis across the southeast Bahamas and the Greater Antilles.
Upper level wind speeds will begin to increase in the exit region
starting on Tuesday, causing the trough to transition to a more
neutral tilt thereafter before losing amplitude on Wednesday. This
dynamic pattern will support upper divergence and instability
across the region. Meanwhile, lowered surface pressures driven by
the upper trough will maintain a deeply moist environment. At the
same time, low level troughs will be sustained, leading to the
increase in moisture convergence and cyclonic rotation. Thus,
expect daily moderate total precipitation maxima particularly in
the Bahamas and Cuba. Elsewhere in the Caribbean, weaker moisture
plumes and low level troughs traversing the islands will yield
light daily precipitation accumulations.

Across Central America and Tropical South America...

As the aforementioned negatively tilted upper trough begins to
lose its amplitude, its base will retrograde into the south
Caribbean Sea. This will enhance upper divergence across Colombia
and Venezuela while increasing subsidence across Central America
on Tuesday and Wednesday. Along the Caribbean coast of Central
America, the low level conditions will drive the precipitation
patterns. Moisture pooling combined with orographic effects will
further enhance precipitation chances, yielding a moderate total
precipitation maxima across Costa Rica and Panama over the next
three days.

On Wednesday, a low level trough wave will move west of the Andes,
significantly increasing low level moisture convergence. The
arrival of the trough is expected to intensify the Panamanian
trough, strengthening low level cyclonic rotation at the low
levels. Elevated total precipitation maxima is likely with these
conditions along the Pacific coast of Colombia. Meanwhile, a
series of tropical waves will be increasing precipitation chances
across the Amazon Delta, Guianas, and Venezuela for the next three
days, yielding moderate total precipitation maxima.

Another region of interest is the western Amazon Basin. On Monday,
an upper level trough will cross the Andes from west to east,
supporting upper divergence across the jungle. In the low-to-mid
levels, dominant easterly winds will assist the transport of
moisture into the region, yielding elevated rainfall accumulations
on Monday. Meanwhile, in the central Amazon, expect the
propagation of a series of low level trough on Tuesday and
Wednesday. These features will support the development of
thunderstorms and increase moisture convergence leading to
moderate rainfall accumulations.

Elsewhere in tropical South America, the presence of the
Intertropical Convergence Zone (ITCZ) near the Amazon Delta will
continue to support daily thunderstorms and moderate rainfall
accumulations. Otherwise, daily diurnal showers and thunderstorms
will be likely across the rest of the region.


Positions of Tropical/Easterly Waves Initialized at 12 UTC
Type SOF INIT  19/00 19/12  20/00  20/12  21/00  21/12  22/00 
22/12
TW   10N  24W   27W   31W    35W    39W    43W    46W    49W    53W
TW   07N  53W   56W   59W    61W    64W    67W    69W    72W    74W
TW   10N  79W   80W   81W    83W    85W    87W    90W    92W    94W
TW   12N  94W   97W   100W   103W   107W   110W   113W   116W   ---



Tinoco-Morales...(WPC)