Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
121 PM EST Thu Dec 04 2025

Forecast Bulletin 04 December 2025 at 1815 UTC:

A low level trough will continue to move across the Caribbean Sea
through the forecast cycle. On Thursday, the low level trough will
be propagating across the ABC islands and will bring with an
increase in moisture convergence and low level cyclonic flow. This
will favor the development of showers and thunderstorms across the
islands with total precipitation accumulations ranging from 15 to
25mm. This trough will begin to move over the Providencia and San
Andres islands early Saturday morning and continue moving into the
Caribbean coast of Nicaragua through the day on Saturday. Thus,
expect an increase in precipitation coverage across the islands
late Friday evening and into Saturday. Meanwhile, on the
Nicaraguan Caribbean coast, precipitation chances will begin to
increase after Saturday morning. On Saturday, expect accumulations
of 15 - 30mm across the islands and decreasing thereafter. Across
northeast Nicaragua and southern Nicaragua, a total precipitation
maxima of 15 - 30mm is likely on Saturday.

Across Trinidad and Tobago and the Guianas, a series of low level
troughs will be moving across the region for the next three days.
As the aforementioned low level trough moves into the interior of
the Caribbean Sea on Thursday afternoon, there will be a decrease
in precipitable water across the southern windward islands in the
Lesser Antilles and Trinidad and Tobago. Across the Guianas, a
long fetch moisture tongue that is extending from the central
Atlantic Basin will remain in the region through the forecast
cycle. Embedded within this plume, expect the development of low
level troughs. These troughs will enhance precipitation chances
across this region, especially for Saturday when precipitation
accumulations of 20 - 45mm are possible. Upper divergence will
also be present in the area and will be primarily sustained by
convective outflows.

Another region of interest in tropical South America is
north-central Brasil. Upper diffluence will be present across this
region and will positively enhance divergence. In the low levels,
expect the daily development of the nocturnal low level jet over
eastern Colombia, which will favor an increase in cyclonic
rotation to its east, primarily across southern Venezuela and
Brasil. The greatest precipitation impacts will be observed on
Thursday and Friday, where total precipitation maxima will exceed
40mm. By Saturday, the region of greatest precipitation impact
will shift into central Brasil, where a mid-level trough will also
be present. The enhancement in vertical ascent, the presence of
deep moisture, and instability will yield a total precipitation
maxima of 20 -35mm. In northwest Colombia, expect the Panamanian
trough to drive precipitation processes for the next three days.
Daily northerly low level flow into the Andino region will support
orographic lift and moisture convergence. On Thursday, a mid-level
trough associated with the aforementioned Caribbean Sea low level
trough will help enhance vertical ascent across this region. Low
level wind speeds will temporarily decrease on Friday before
gaining intensity on Friday. Moisture convergence will be present
on Friday as well as local and orographic effects. Thus, a total
precipitation maxima of 20 - 45mm are possible for Thursday and
Saturday.

In Mexico, an upper-level trough embedded within the subtropical
jet stream will begin to interact with the polar jet stream and
favor the development of a potent jet streak max that will be
spanning across Baja California, Sonora, Sinaloa, and Chihuahua
through the next three days. This trough will become increasingly
negatively titled and will support the sustenance of upper
divergence. In the mid-levels, there will also be a series of
shortwave troughs propagating across the region and will enhance
vertical ascent and destabilization. Two moisture plumes will be
converging along the western coasts of Mexico. The first plume
will be affecting Sur Baja California, southern Sonora, and
northern Sinaloa on Thursday and Friday before losing definition
late on Friday. Moisture convergence will be enhanced in these
regions during this period and the combination of the mid-to-upper
level pattern will yield to a total precipitation maxima of 20 -
45mm on Thursday across Sinaloa. On Friday, a total precipitation
maxima of 20 - 35mm will be possible in this same region. On
Saturday, the secondary moisture plume will begin to affect
Jalisco, Nayarit, and Michoacan and will yield a total
precipitation maxima of 15 - 25mm. At the same time, there will be
a shortwave mid-level trough moving into this region.

Another area of interest in Mexico is the Gulf coasts of
Tamaulipas and Veracruz. A cold front will be moving across
Tamaulipas on Thursday and transitioning into a decaying
stationary front on Friday. There will be a brief period of
easterly low level winds into southern Tamaulipas, northern
Veracruz, and southeastern San Luis Potosi late Thursday and into
early Friday morning. This low level flow will quickly shift to a
southerly direction after the morning. Thus, if any precipitation
does develop, it will likely be attributed to the enhanced lift
provided by the cold-stationary front and orographic enhancement
during this time period.

Elsewhere in the tropical region, expect the presence of low level
troughs to favor the development of precipitation across much of
the region. The diurnal cycle and local effects will positively
contribute to the sustenance of precipitation. Expect an increase
in precipitation in areas where the monsoon trough is present. In
the large scale, there is a kelvin wave and equatorial rossby wave
that are moving across the tropical region currently and will
continue enhancing upper divergence for the next three days.  


Positions of Tropical/Easterly Waves Initialized at 12 UTC
TYP SOF  INIT  05/00  05/12  06/00  06/12  07/00  07/12  08/00
--  --    --    ---    ---    ---    ---    ---    ---    ---  

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

Tinoco-Morales...(WPC)