Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
327 PM EDT Tue Aug 18 2026

Forecast Bulletin 18 August 2026 at 1925 UTC:

Persistent upper-level dynamic support and highly enhanced
precipitable water (PWAT) across eastern Honduras to Panama will
sustain broad high rainfall totals.

Mexico and Northern Central America . . .
A series of lower-level troughs and topography will support
moisture convergence over southern Mexico and northern Central
America today. Moderate upper-level support and daily heating will
favor isolated areas of convective rain. Over northwestern Mexico,
a well-structured mid-to-upper-level low is increasing instability
and rainfall totals; however, this region will exit the region
later today. North America Monsoon will support precipitation
elsewhere across northwestern to western Mexico throughout the
next few days. Upper divergence will develop and sustain deep
ascent later Wednesday into early Thursday over the southwest. A
couple of tropical waves will promote moisture convergence and
lower-level instability to bring a significant increase of
rainfall maxima.

The Bahamas and Caribbean . . .
A tropical wave over the Leeward Islands today will move
west-northwest through Wednesday and Thursday, reaching
Hispaniola. An upper-level trough will track westward along with
this wave, providing upper-level ventilation to support deep
convection. Some deep convection is expected over the Windward and
ABC Islands region through Wednesday afternoon.
A mid-level ridge of high pressure north of the Greater Antilles
will follow the passage of the tropical wave from Thursday into
Friday. Consequently, the eastern Caribbean will experience drier
air and lower capping inversions.
From Wednesday into Thursday, a tropical wave moves toward the
Greater Antilles accompanied by higher moisture. An upper-level
low deepening west of Hispaniola will support deep convection.
Localized rainfall maxima of 20-45 mm are likely over Hispaniola
on Thursday. Daily accumulation of 5-10 mm, with maxima of 15-20
mm, is forecasted over the next few days elsewhere in the region.
Northern South America and Southern Central America . . .
The monsoon trough and Intertropical Convergence Zone patterns
will support strong low-level moisture convergence across southern
Central America. In the upper-level, a steady region of wind
divergence will persist over Nicaragua to Panama through the next
few days. This setup will support rainfall total maxima of 30-60
mm today. Totals will decrease slightly on Wednesday and Thursday,
but an incoming tropical wave will increase low-level moisture
convergence further east into the west of Colombia, spreading the
area of significant rainfall. The passage of a tropical wave over
Orinoquia will support convective precipitations today. A series
of lower level troughs, humidity advection, and diurnal heating
will trigger showers across central to western Amazon through the
next three days, and over Orinoquia after Wednesday.


Tropical Waves Initialized at 12 UTC:
Typ SOF INIT 19/00 19/12 20/00 21/12 22/00 22/12 23/00 23/12
TW 15N  32W  35W  38W  41W  44W  47W  50W  53W  56W
TW 18N  65W  69W  72W  75W  78W  81W  84W  88W  93W
TW 15N  82W  86W  90W  93W  97W  100W  Abs  ---   ---
TW 13N  89W  92W  95W  97W  101W  104W  107W  112W  115W
TW 11N  102W  105W  108W  109W  111W  113W  116W  119W Abs
TW 14N  110W  113W  116W  119W  Exits  ---  ---  ---  ---

Sanchez-Perez...(WPC)

Tinoco-Morales...(WPC)