Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
239 PM EST Fri Jan 23 2026

Forecast Bulletin 23 January 2026 at 1940 UTC:

Over the next three days, the most significant rainfall is
expected across northwestern Mexico, where multiple atmospheric
features will combine to support periods of moderate to locally
heavy precipitation. The primary focus includes the Baja
California Peninsula, southern Sonora, and the Sierra Madre
Occidental, where storm-total rainfall amounts may reach 30 - 60
mm, with localized maxima of 50 - 100 mm, particularly across
southern Sonora. At higher elevations along the Sierra Madre
Occidental, a portion of this precipitation may fall as mountain
snow. All rainfall amounts referenced represent accumulated totals
from today through early Monday morning.

Rainfall across northwestern Mexico will be driven by the
interaction of a strong upper-level trough, a cold front currently
moving into the region, and a surge of deep tropical moisture from
the eastern Pacific. This frontal boundary will continue its
southward progression through Saturday while gradually weakening;
however, it will still provide sufficient low-level instability to
support convective development. At the same time, anomalously high
moisture, exceeding two standard deviations above climatological
normals, will be advected inland from the Pacific. This moisture
transport will be enhanced by a westerly low-level jet, allowing
for efficient rainfall production. The combination of large-scale
ascent, frontal forcing, and terrain effects will favor periods of
heavy rainfall, especially along windward mountain slopes.

At upper levels, an upper-level trough crossing northwestern
Mexico will be accompanied by a strong jet streak, with wind
speeds potentially exceeding 100 kt. This feature will enhance
divergence aloft and support deeper, more organized convection
across the region. The coupling of this upper-level support with
the weakening frontal boundary, deep Pacific moisture, and
favorable low-level flow will also act to promote the
aforementioned heavy rainfall expected across northwestern Mexico
through Saturday evening.

A separate cold front will move southward from the United States
into northern and northeastern Mexico during the weekend. This
boundary is distinct from the front affecting northwestern Mexico
and is expected to have a more limited impact. While it may lead
to increased cloudiness and scattered precipitation as it
progresses southward, rainfall amounts across northeastern Mexico
are expected to remain modest compared to those observed in the
northwest. As this front advances, the western portion of the
front will become stationary and it is forecast to weaken and
gradually dissipate along the Sierra Madre Oriental by Monday.
That said, a portion of the cold front will continue moving south
and is expected to be over Veracruz by Sunday evening.

Across tropical South America, the most persistent rainfall over
the next three days is expected across central Brazil, southern
Venezuela, and the Amazon region of Peru, with additional activity
across western Colombia and Ecuador. In these areas, abundant
low-level moisture combined with embedded low-level troughs will
support repeated convective development. Rainfall in western
Colombia and Ecuador will also be influenced by the ITCZ and
monsoon trough over the eastern Pacific, favoring locally heavy
totals along the Pacific-facing slopes.

Across the Caribbean and Central America, a strong subtropical
high over the central to eastern Atlantic will continue to
dominate the low-level pattern, maintaining persistent easterly
trade winds through the weekend. This regime will promote
generally stable conditions and limit widespread rainfall across
much of the region. While isolated passing showers are expected,
most locations will see light accumulations. However, localized
higher totals remain possible in parts of the Lesser Antilles and
northeast Caribbean, where three-day accumulations may exceed 35
mm in isolated areas. Along the Caribbean coast of Nicaragua,
interaction between low-level moisture and onshore flow may
support more persistent rainfall, with totals generally reaching
30 - 50 mm over the three-day period.


Alamo...(WPC)