845
FXCA20 KWBC 201838
PMDCA

Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
238 PM EDT Thu Aug 20 2026

Forecast Bulletin 20 August 2026 at 1840 UTC:

Across Mexico...
Across the western Pacific coast, starting on Friday, the northern
periphery of an upper ridge will begin to see an increase in wind
speeds. The north-exit region of the ridge will be interacting
with a preexisting upper trough, which will be located across
northeast Mexico for the next three days. This interaction will
lead to a significant increase in upper wind diffluence across the
western Pacific coast of Mexico and central Mexico for Friday and
Saturday. The dynamic nature of the upper levels will support the
moistening trend across the region and the development of
mid-level shortwave troughs.

With respect to precipitation impacts, conditions will be driven
by local and orographic effects on Thursday for northwest Mexico.
Expect the development of showers and thunderstorms that will
bring isolated moderate total precipitation maxima. By Thursday,
there will be a gradual increase in precipitable water across the
region in response to the upper levels, from northwest Mexico and
along the north and central Pacific coast of Mexico. Thus,
anticipate more widespread precipitation across the coastline and
along the high terrain for Friday and Saturday, where moderate to
enhanced precipitation maxima is likely.

Across Central America and South America...
A series of tropical waves will be traversing the Central America
Isthmus throughout the forecast cycle. The first tropical wave of
interest is currently traversing Costa Rica and south Nicaragua.
This tropical wave is being accompanied by high precipitable water
values and high instability. Instability will decrease subtly as
the tropical wave moves into the Pacific on Thursday afternoon.
Regardless, the environment will still be conducive to showers and
thunderstorms through Friday morning. On Friday, another tropical
wave will be approaching the region and the environment will
remain moist and unstable through the remainder of the forecast
cycle. Additionally, the Caribbean Low Level Jet (CLLJ) will be
converging into the region and favoring enhanced low level
cyclonic rotation across Costa Rica and Panama, reinforcing ascent
in the region. Daily moderate to enhance total precipitation
maxima is expected across Nicaragua and Costa Rica.

With the passage of these tropical waves, expect a moistening
trend across the Pacific coasts of Colombia and Ecuador. Daily
diurnal showers and thunderstorms are likely across Ecuador and
the south Colombian coast. Across the north-central coastline,
there will be periods where the low level wind flow will be
orthogonal to the local orography, leading to elevated
convergence. Overall, daily enhanced total precipitation maxima is
likely in this region through the forecast cycle.

Across the Amazon and northern South America, seasonal conditions
will persist through the majority of the region. An area of
interest is northeast Colombia and Venezuela, which will be
influenced by the passage of tropical waves. At the same time,
expect the development of local surface to low level troughs that
will continue to support the development of showers and
thunderstorms.

Across the Caribbean...

An upper-level low north of Puerto Rico, in combination with an
upper-level trough over Panama, is supporting upper-level
divergence over the eastern Caribbean today, Thursday. The
upper-level trough will move west-northwestward over the next few
days, supporting upper-level ventilation over the central and
western Caribbean.


A tropical wave over the Lesser Antilles, embedded in limited
moisture, is producing isolated showers, with maxima around 10 mm
over the southernmost islands for today. As the wave advances into
the central Caribbean on Friday, isolated convection is expected
across the Leeward Antilles, with scattered showers and
thunderstorms becoming more likely over Hispaniola. By Saturday,
increasing low-to-mid-level moisture associated with the wave
should favor a more active convective pattern, with scattered
showers and deeper convection developing as the wave crosses
Jamaica and eastern Cuba.


Tropical Waves Initialized at 12 UTC:
Typ SOF  INIT  21/00  21/12  22/00  22/12  23/00  23/12  24/00
24/12
TW  20N  42W   44W    47W    50W    53W    56W    59W    61W    64W
TW  20N  52W   55W    58W    61W    64W    67W    70W    74W    78W
TW  15N  58W   63W    66W    70W    74W    77W    80W    83W    86W
TW  15N  75W   77W    80W    83W    86W    88W    90W    93W    95W
TW  11N  98W   100W   102W   104W   106W   109W   112W   115W
116W
TW  12N  111W  112W   114W   116W   117W   EXIT   ---    ---    ---

Tinoco-Morales...(WPC)
Sanchez-Perez...(WPC)
Luciano...(MDC)


$$