694
FXCA20 KWBC 171817
PMDCA

Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
216 PM EDT Fri Jul 17 2026

Forecast Bulletin 17 July 2026 at 1820 UTC:

Mexico...
Over the region of Mexico, much of the heaviest rainfall is
expected over the west and into the southern portion of the
country, while the northeast sector remains relatively dry over
the next three days. On Friday, an upper trough over the southern
United States connects with an upper trough over the Baja
California Peninsula, and they interact with a strengthening ridge
over the Eastern Pacific. Much of the divergence aloft is expected
along the Sierra Madre Occidental, and will fuel much of the
convection that develops in the afternoon and into early Saturday.
In terms of precipitation, the area will see a modest increase in
available moisture with the passing of tropical waves to the
south, advecting moisture along the continental Mexican Pacific
coast. Expect maxima to reach around 20-35mm from Sonora through
north Jalisco. On Saturday, a disorganized upper level pattern
develops, as the upper ridge over the East Pacific meanders west,
favoring entry of a trough from western Texas-USA, favoring modest
divergence along the northern sector of the Sierra Madre
Occidental region Saturday evening and into the night. By late
Saturday night into Sunday early morning, divergence is present to
the south, where a tropical wave has passed over southwest Mexico,
approaching a second wave with the ends of being absorbed into one
tropical wave by the morning of Sunday. The moisture associated
with this wave will favor light to moderate showers from Guerrero
into Jalisco, while the Sierra Madre Occidental can expect
generalized maxima of 20-45mm on Saturday. On Sunday, the combined
tropical waves continue west over the Pacific Ocean, while another
tropical wave propagates over Oaxaca and Guerrero during the day.
Expect light showers as low available moisture is expected. To the
northwest, a strengthening ridge over the western United States
will block a meandering shortwave trough over the sector, when it
will favor enhanced divergence aloft. Expect moisture to
convergence in this region and maxima of 25-50mm on Sunday into
early Monday.

Central America...
The region is beginning to see the fast approach of dry air in
association with the Saharan Air Layer and dry air advection over
the Atlantic Ocean and Caribbean Sea. The zonal flow at the south
and periphery of the Atlantic high pressure system is favoring
this advection in the mid levels, and increasing the presence of
trade wind inversions at around 750hPa. This will limit the
development of deep convection for much of the eastern sector of
Central America on Friday. Expect light precipitation from Belize
and Guatemala through Nicaragua. The available moisture entering
the region is remaining over Costa Rica, where it converges along
the mountain range and favors maxima of 20-35mm on Friday. On
Saturday, the relative humidity in the region is expected to
decrease to below 40% from Belize/Guatemala through Nicaragua.
Trace to light precipitation could be present in this region, but
convection could remain shallow and favor low total rainfall. To
the south, moisture also decreases in the region, and could favor
a generalized maxima of 15-25mm in Costa Rica and Panama. By
Sunday, much of the northern Central America sector could expect
decreased precipitation, a trace amount to about 10mm with the low
amount of available moisture. In contrast, eastern Costa Rica and
into Panama, a tropical wave that has absorbed a secondary
tropical wave over the west Caribbean will increase the amount of
moisture converging in the region, favoring maxima of 25-50mm.

Caribbean and The Bahamas...
The Atlantic high-pressure system is expected to remain nearly
stationary during the next two days. By Sunday, it is forecast to
gradually weaken while slowly shifting westward. Furthermore, the
Saharan Air Layer will remain the dominant weather feature across
the Caribbean Basin, combined with a relatively strong low-level
inversion below 800hPa over most of the region. As a result,
generally dry weather conditions are expected to prevail. However,
two tropical waves will traverse the Caribbean later today and on
Saturday, bringing some changes, primarily across the southern
Caribbean and portions of the Greater Antilles. These waves are
expected to temporarily weaken the influence of the Atlantic
high-pressure ridge across the Caribbean. The first tropical wave
is forecast to move across Hispaniola later today, temporarily
weakening the low- to mid-level inversion. Combined with limited
moisture plumes moving across the Greater Antilles, this may
support the development of isolated convective precipitation over
the Dominican Republic and nearby areas. The second tropical wave
will enter the Caribbean later tonight, with most of its
associated moisture remaining south of 13N. As it moves across the
eastern Caribbean on Saturday, it is expected to temporarily relax
the pressure gradient, particularly across the ABC Islands and
surrounding waters. As a result, wind speeds are expected to
decrease over this area. By Sunday, the tropical wave is forecast
to be absorbed by the tropical wave already moving through the
central Caribbean, as the strong Caribbean Low-Level Jet (CLLJ)
accelerates its westward movement.During the next three days the
available low- and mid-level moisture advection associated with
these tropical waves may support isolated convective
precipitation, mainly across the southern Caribbean. Elsewhere
across the Caribbean Basin, precipitation is expected to remain
limited to isolated light showers producing only trace rainfall
amounts.

North South America...
The northern South America region will see a similar drying trend
as Central America. The passing of tropical waves to the north
will assist with the advection of moisture reaching the northwest,
and the interaction with the Andes Mountains will favor moisture
convergence and orographic lift, fueling convection primarily from
Colombia. The exception will be on Sunday into Monday, where an
amplified tropical wave enters Panama, allowing for cyclonic
rotation into western Colombia, and enhancing moisture convergence
along the Pacific coast of the country. Expect maxima of 30-60mm,
with a potential for locally higher totals. The Inter-tropical
Convergence Zone (ITCZ) is positioning over the northern coast of
Guyana and will meander north into Trinidad and Tobago over the
next three days. The placement of the ITCZ and the addition of the
propagating tropical waves will amplify convection in the region,
primarily on Friday and Saturday. However, the fast progression of
these waves will give way for light to moderate precipitation
totals daily over the next three days. Ridging over the northern
portion of the continent will continue to favor subsidence over
the next three days, as it meanders west ward from east Brasil
into the Amazon Basin.

SOF INIT 18/00 18/12 19/00 19/12 20/00 20/12 21/00 21/12
21N 24W  26W  28W  30W  32W 34W  37W 39W 41W
21N 43W  48W  53W  57W  63W 68W  73W 78W 82W
19N 57W  63W  69W  73W  ABS ---  --- --- ---
21N 67W  70W  73W  76W  79W 83W  87W 90W 93W
19N 87W  90W  93W  97W 100W 102W 104W 106W 108W
20N 98W  101W 103W 105W ABS  --- --- --- ---
20N 105W 107W 108W 109W 110W 112W 114W 116W EXITS

Luciano...(MDC)
Castellanos...(WPC)


$$