129
FXCA20 KWBC 171851
PMDCA

Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
251 PM EDT Mon Aug 17 2026

Forecast Bulletin 17 August 2026 at 1900 UTC:

A series of tropical waves will be moving across the region that
will enhance precipitation for the next three days. The first
tropical wave of interest is currently moving across the Caribbean
coasts of Honduras, Nicaragua, and Costa Rica. The wave will be
moving across the Yucatan Peninsula on Tuesday and arriving into
south Mexico on Wednesday. In the vicinity of the tropical wave,
expect elevated precipitable water values. Also contributing to
the above normal precipitable water values is the presence of an
upper trough across the Gulf.

Starting this afternoon, the upper trough in the south Gulf will
begin to interact with a strengthening anticyclone in the western
Caribbean Sea, which will promote an increase in upper level wind
speeds and upper diffluence with this pattern continuing into
Tuesday. This dynamic upper level regime across the Yucatan will
continue to support moisture pooling in the region. By Wednesday,
an upper level anticyclonic pattern will be developing across
north Central America, the Yucatan Peninsula, and south Mexico and
it will be favoring upper divergence across central Mexico and
into the central Gulf coast region. Overall, expect instability to
increase with the approach of the tropical wave. For the next
three days, daily moderate total precipitation maxima are likely
in the vicinity of the tropical wave.

Another region of interest in Mexico is the northwest. Through
Tuesday morning, expect a mid-level trough to be present across
northwest Mexico, which will help destabilize the environment. At
the same time, upper level speed divergence will be developing
along the northwest Gulf of California and Pacific coast.
Furthermore, the environment will be moist in the low and mid
levels. These conditions will favor the development of monsoonal
convection across the higher terrain of northwest Mexico where
total precipitation maxima will surpass 30mm. Thereafter, there
will be a gradual decrease in precipitation across north Mexico as
the aforementioned upper trough moves overhead. This trough will
help transport a drier air mass from the northern Gulf into the
region and thus contributing to a subtle drying trend for Tuesday
and Wednesday. Meanwhile along the Gulf of California and Pacific
coasts, daily isolated showers and thunderstorms will continue as
low level moisture will still be present in the region.

A broad low level cyclonic circulation pattern is currently
present across the southwest Caribbean Sea, which is sustaining
long fetch westerly low level winds into the north and central
Pacific coasts of Colombia and easterly low level winds into
Nicaragua, Costa Rica, and Panama. Its structure will weaken by
Tuesday morning as another tropical wave moves across the region.
This tropical wave is currently approaching the Panama Bight from
Colombia. Embedded within this wave are multiple shortwave troughs
in the low and mid-levels and vorticity maxes that will support
convection for today and Tuesday. The tropical wave will arrive
into the Caribbean coasts of Nicaragua and Costa Rica on Tuesday.
There will be a significant increase in precipitable water with
the arrival of the wave. Easterly low level winds will be
prominent through Wednesday morning but the most significant
moisture convergence is anticipated for Tuesday when the mid-level
moisture content is also anticipated to increase. With respect to
precipitation impacts, expect enhanced total precipitation maxima
along the Pacific coast of Colombia and the northwest Caribbean
coast on Monday. Also expect moderate total precipitation maxim
across Panama and Costa Rica for Monday. By Tuesday, precipitation
impacts will decrease across Colombia and a localized maxima is
anticipated along the eastern border of Nicaragua/Costa Rica where
local effects will reinforce surface to low level convergence.
Elevated total precipitation maxima is likely in this region.
Precipitation will be ongoing into Wednesday as the region will
remain moist, though, precipitable water values will decrease.
Regardless, moderate total precipitation maxima is still likely
across the Nicaragua/Costa Rica border.

The last tropical wave of interest is currently approaching the
Lesser Antilles and will continue to sustain convection through
the day. The northern extension of the wave will become
disconnected from the main system and will be primarily influenced
by the subtropical surface to low level ridge. The remnant of the
tropical wave will continue to move across the Greater Antilles
for the next three days, bringing with moisture advection and
increasing instability. Thus, anticipate an increase in
precipitation with the approach of this tropical wave.


Tropical Waves Initialized at 12 UTC:
Typ SOF  INIT  18/00  18/12  19/00  19/12  20/00  20/12  21/00
21/12
TW  18N  58W   62W    66W    70W    73W    76W    79W    82W    85W
TW  14N  80W   82W    84W    86W    88W    92W    96W    ABS    ---
TW  11N  95W   99W    101W   105W   107W   109W   111W   113W
115W
TW  17N  103W  107W   110W   114W   116W   EXIT   ---    ---    ---
TW  22N  83W   86W    89W    92W    94W    97W    100W   103W
105W


Tinoco-Morales...(WPC)



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