Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
113 PM EDT Tue Oct 21 2025

Forecast Bulletin 21 October 2025 at 1715 UTC:

Through the forecast cycle, expect Tropical Storm Melissa to be
the main contributor to precipitation across the Greater Antilles.
For more information regarding the track and intensity, please
refer to
https://www.nhc.noaa.gov/graphics_at3.shtml?start#contents.

In the Caribbean and Bahamas...
Moist easterly low level winds will dominate across southern
Hispaniola and Puerto Rico, potentially contributing to an
enhancement in moisture convergence. There remains uncertainty in
the track of Tropical Storm Melissa within the global model
guidance and a subtle shift to the west may decrease precipitation
totals across the Dominican Republic and increase accumulations
across Jamaica and Haiti. Regardless, still anticipate significant
precipitation accumulations across Hispaniola, especially in the
southern region. Orographic effects may contribute to an
enhancement of low level moisture convergence and help yield total
precipitation maxima of over 150mm for the next three days across
south - central Hispaniola. Precipitation impacts should begin on
Tuesday and will increase substantially by Wednesday.

Across Jamaica, expect an increase in moisture in the area by
early morning Wednesday. Significant moisture convergence is
likely across the northeast portions of Jamaica and southeast
Cuba, promoting total precipitation maxima that may exceed 90mm
for the next three days. The period of greatest precipitation
impact, for now, appears to begin late Wednesday evening and
continue into Thursday for Jamaica and Cuba. Thereafter,
uncertainty grows in the track of the system. Note that some upper
level divergence affiliated to an upper level trough may help
favor upward development for convection across southeastern Cuba.
This upper level trough may also assist in supporting deep
convection across the southern Bahamas, but higher uncertainty
remains for this region and its direct impacts with Tropical Storm
Melissa. Despite this, still anticipate an increase in moisture in
this sector which may favor the development and sustenance of
convection, especially after Thursday.

Another region that may be impacted by Tropical Storm Melissa is
Puerto Rico. Some moisture convergence is possible as low level
easterly winds may dominate across the region while the system
skirts just to the south of the island. This increase in low level
convergence will favor the increase in precipitation
accumulations, particularly across the southern and southeastern
areas of the island. Precipitation accumulations for the next
three days may exceed 50mm across the aforementioned regions.

In Mexico, Central America, and South America...

Across Mexico and Central America, the base of an upper level
trough will be located across the Yucatan Peninsula, Guatemala,
and Belize on Tuesday, favoring the increase in upper level
divergence and general ascent in this region. At the low levels,
expect enhanced north-northeasterly flow to converge with local
orography which will also support an increase in moisture
convergence. This trough is expected to continue moving eastward
into the greater antilles and its impacts across north Central
America and southern Mexico will diminish after Wednesday. Across
the interior of Mexico, an upper level ridge will suppress
precipitation across much of the nation, if any precipitation does
develop, it will likely be attributed to propagating low level
troughs, the diurnal cycle, and local effects.

Across Nicaragua, Costa Rica, and Panama, the monsoon trough will
be the main contributor to the development of convection in this
region. Onshore flow is anticipated for Tuesday and Wednesday
across the Caribbean coasts of Nicaragua and Panama. Thereafter,
the lowering pressures in the northern Caribbean Sea will favor
increasing southwesterly low level wind flow across the southern
half of the basin. This may promote an increase in moisture across
the Pacific coasts of Panama and Costa Rica starting Thursday.

In South America, a seasonal precipitation pattern will continue
for much of the subtropics. Low level troughs will enhance
moisture convergence and could potentially interact with the
diurnal cycle and local effects, favoring an increase in
precipitation totals across the basin. A low level feature of
interest is a trough that is currently moving across the Guianas.
This trough may yield an increase in precipitation totals for
Tuesday and Wednesday. Another area of interest is northern
Venezuela, Colombia, and Brasil. Falling pressure values to the
north will favor increasingly southerly flow across this region,
especially for Wednesday and Thursday. This flow will contain high
precipitable water and could enhance moisture convergence and
orographic effects. Thus, expect increasing total precipitation
maxima across this sector for Wednesday and Thursday. Lastly,
Colombia will also be indirectly affected by Tropical Storm
Melissa, where increasing onshore low level flow will favor daily
total precipitation maxima exceeding 60mm. Minimal shear will be
present in this region and could sustain deep convection.


Positions of Tropical/Easterly Waves Initialized at 12 UTC
TYP SOF INIT  21/00  21/12 22/00  22/12  23/00  23/12  24/00
EW  16N 100W  103W   106W  108W   110W   Low    Low    Low

For the latest available charts please visit:
https://www.wpc.ncep.noaa.gov/international/crb_day1-3.shtml

Tinoco-Morales...(WPC)