924
FXCA20 KWBC 031657
PMDCA

Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
1156 AM EST Wed Dec 03 2025

Forecast Bulletin 03 December 2025 at 1700 UTC:

In the Lesser Antilles, a low level induced trough that is
associated with a positively tilted upper trough is currently
moving across the windward islands and will bring an increase in
low level moisture convergence. Expect convection to persist on
Wednesday and decrease in coverage through the night. Still, there
is a potential for the development of isolated convection during
the night into early morning hours of Thursday as mid-level
troughing will be present across the region. Thereafter, the upper
level trough supporting the induced low level trough will begin to
lose definition and move east into the Atlantic Ocean Basin. A
total precipitation maxima of 20 - 45mm is expected from St.
Vincent and the Grenadines and into northwest Guyana. By Thursday,
the induced trough will begin to lose definition. There is also
another low level trough, that will be located near 65W, and
trailing behind the induced trough. This trough is expected to
continue propagating into the western Caribbean Sea. At the 925 -
850mb layer, average winds will begin to accelerate behind the
trailing low level trough and will support a faster propagation
speed. These two low level features will enhance low level
cyclonic rotation and moisture convergence across the ABC islands
and will yield a total precipitation maxima of 15 - 25mm for
Thursday. Across the Guianas and Trinidad and Tobago, still expect
the presence of easterly low level winds, which will support
moisture convergence and will favor a total precipitation maxima
of 20 - 35mm for Thursday. Another low level trough will be moving
into the Guianas on Friday and it will have accompanying
precipitable water values exceeding 57mm. These conditions will
yield a total precipitation maxima of 30 - 60mm. Note that there
may be upper divergence in the area due to convective outflows,
which will sustain the development of deep convection in the
region.

Elsewhere in the Lesser Antilles and Greater Antilles, expect a
series of low level troughs to move into the islands daily. These
troughs will provide additional low level cyclonic rotation and
subtle increases in available moisture convergence. The diurnal
cycle, local effects, and orographic enhancement will help
increase precipitation accumulations with the traversal of the low
level troughs across the islands.

Across north-central Brasil, an upper level diffluent wind regime
will be continuing through Thursday and will positively contribute
to the sustenance of upper divergence across the region. In the
mid-levels, a series of shortwave troughs will also be moving
across this region. Thus, expect a daily total precipitation
maxima of 30 - 60mm for Wednesday and Thursday. On Friday, the
area of greatest precipitation impact will be across northwest
Brasil where speed divergence is expected to dominate. This will
favor a total precipitation maxima of 20 - 35mm. Another region of
interest in tropical South America is north Colombia where the
Panamanian low level trough will be the main driver for the
initiation of convection in the region. On Wednesday, precipitable
water values will exceed 50mm. The low level wind flow will be
rather weak, ranging from 5 to 10 knots. Thus, convection that
does develop will be mostly driven by local effects and the
diurnal cycle. Precipitation accumulations will range from 20 -
45mm on Wednesday. By Thursday, isolated accumulations of up to
45mm is possible across the Pacific coast of Colombia, being
influenced by local topographical effects and the diurnal cycle.

Another area of interest is Sinaloa and Chihuahua in Mexico. A
mid-to-upper level trough is expected to become positively tilted
and will remain semi-stationary off the Pacific coast of Mexico.
This trough will be interacting with the polar jet stream that
will be located across the continental United States and will
induce the development of an upper jet streak max across Sonora
and Chihuahua. This will trigger the development of mid-level
shortwave troughs and low level troughs through the forecast
period. In the low levels, a long fetch moisture tongue will begin
to move into the region on Wednesday where a westerly low level
flow will be converging with the coasts of Sinaloa and Nayarit. By
Thursday, the low level flow will be from the southwest and wind
speeds will increase. These conditions will favor increasing
moisture convergence across the region and will be further
supported by the mid and upper level pattern. Thus, we expect
increasing chances for precipitation starting on Thursday. A total
precipitation maxima of 20 - 45mm is possible across Sinaloa and
Chihuahua while another region of 20 - 35mm is expected across
north-central Chihuahua. By Friday, precipitation accumulations
will begin to decrease across Chihuahua as the moisture tongue
will also lose definition. Another long fetch moisture tongue will
begin to move into Jalisco, Colima, and Michoacan on Friday. This
will favor increasing low level moisture convergence and
precipitation accumulations. Elsewhere in Mexico and Central
America, expect seasonal conditions to prevail for the rest of the
forecast cycle. There will be a significant decrease in available
moisture across this sector.

Positions of Tropical/Easterly Waves Initialized at 12 UTC
TYP SOF  INIT  04/00  04/12  05/00  05/12  06/00  06/12  07/00
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For the latest available charts please visit:
https://www.wpc.ncep.noaa.gov/international/crb_day1-3.shtml

Tinoco-Morales...(WPC)
$$