161 FXCA20 KWBC 151902 PMDCA Tropical Discussion - International Desks NWS Weather Prediction Center College Park MD 301 PM EDT Thu Oct 15 2026 Forecast Bulletin 15 October 2026 at 1902 UTC: An upper-level trough moving across the U.S. today will be cut off on its southwestern flank, remaining as cyclonic circulation centered over southern California while the remainder continues eastward Friday into the weekend. This splitting will enhance upper-level divergence over northwestern Mexico supporting strong upward motion later today into Friday. The mid-level moisture flow extending from Tropical Storm Simon into North America will be constrained and eventually cut off as strong northerly winds develop, saturating the air mass over this region while increasing cyclonic potential vorticity (PV). Strong low-level moisture convergence will be supported by the associated cold front moving beneath. Heavy rainfall is likely over Chihuahua later today into Friday with maximum daily rainfall accumulations of 30-60 mm. On Saturday, mid-level flow will drive a moisture plume further west to interact with the existing dynamics, triggering showers over the Baja California Peninsula and Sonora. Off southwestern Mexico, Hurricane Trudy will approach the southwestern coast of Mexico supplying the region with abundant moisture across the Pacific coast into the Gulf coast by the weekend. A tropical wave crossing the western Caribbean will support the low-level moisture convergence. A series of mid-level shortwaves will increase PV over the northwestern Caribbean to trigger isolated heavy showers in Cuba and from northeastern Nicaragua to Quintana Roo today. The interaction between Hurricane Trudy approaching from the south, the tropical wave from the east and the cold front from the northwest will create a pool of abundant moisture and dynamic instability, leading to widespread thunderstorms extending from the Mexican Gulf Coast to western Honduras and along the Sierra Madre del Sur coast on Friday and Saturday. As the cold front moves further southeast on Saturday, moderate to locally heavy storms will develop from western Cuba to the northern Bahamas, where marginal risk of severe weather is forecast. A perturbed low-level flux moving across northern South America will create a series of low-level troughs from the eastern to the western Amazon basin today, providing significant low-level moisture convergence. Scattered areas of mid-level PV will support upward motion development while a dense plume of saturated air develops from Orinoquia to the southwest, over western Amazon Basin, and southeast into the central Amazon basin. These mid-to-lower level dynamics will continue over the next few days, while upper-level divergence will develop later Friday into Saturday across Orinoquia into the western and central Amazon Basin, supporting deep convection development. Maximum daily rainfall accumulations of 20-35 mm are forecast on Friday and up to 40 mm on Saturday. Mid-level flow across northern South America will advect some moisture and PV from the Amazon basins over the Andes into the Pacific region later today, while a meandering west-component low-level inland flow develops along the northwestern South American coast. Heavy storms will develop later today along the Colombian Pacific coast and the Andes from Colombia to northern Ecuador, continuing on Friday and Saturday, when the highest accumulation totals will remain over Colombian. Tropical Waves Initialized at 12 UTC: TYP SOF INIT 16/00 16/12 17/00 17/12 18/00 18/12 19/00 19/12 TW 13N 32W 34W 37W 41W 43W 46W 49W 51W 54W TW 17N 59W 63W 65W 67W 70W 73W 75W 77W 79W TW 17N 82W 85W 87W 88W 88W 89W 90W 92W 93W Sanchez-Perez...(WPC) $$  260 FXCA20 KWBC 151904 PMDCA Tropical Discussion - International Desks NWS Weather Prediction Center College Park MD 304 PM EDT Thu Oct 15 2026 Forecast Bulletin 02 October 2026 at 1900 UTC: Today (Friday), locally heavy rainfall will remain a concern across southern Mexico and Pacific Central America. Over the weekend, heavy rain and a few strong thunderstorms are expected over Hispaniola, while moisture shifting toward the western Gulf will increase the rainfall threat along eastern Mexico by Sunday. An upper-level low near the southern Bay of Campeche will drift west to northwest through Sunday. Rainfall will favor its moist periphery, with convergence and terrain helping focus convection across southern Mexico. Deep moisture extending from the western Caribbean into the Gulf will gradually shift westward. By Sunday, southeasterly flow will transport this moisture toward Tamaulipas and Veracruz, increasing the potential for heavy rainfall where coastal convergence and lifting along the eastern slopes overlap. Farther west, afternoon convection will favor the Sierra Madre Occidental and adjacent interior areas, while moisture and terrain continue to support locally heavy storms over Oaxaca and Chiapas. Over Hispaniola, a mid- to upper-level trough will deepen toward the island and develop a closed circulation nearby by Sunday. Relatively cool air aloft above a warm, moist boundary layer will support increasing instability. Daytime heating, mountain circulations, and sea-breeze convergence will favor thunderstorms, with the greatest coverage expected Saturday afternoon and evening over Haiti and the western to central Dominican Republic. Locally heavy rainfall may continue into the night. Additional storms are possible Sunday, although decreasing moisture across eastern Hispaniola should reduce overall coverage. Forecast soundings support vigorous afternoon updrafts, particularly over Haiti. Pockets of drier air above the moist lower levels could strengthen downdrafts, which could allow a few storms to produce strong winds. Brief small hail is possible in the strongest cells, although confidence is lower than for strong gusts. The expected profile favor localized episodes of strong convection. For the 48-hour period from 12Z Saturday, October 3, through 12Z Monday, October 5, rainfall totals of 50-100 mm are possible in the wetter portions of central and northern Haiti and the western to central Dominican Republic, with localized maxima that could surpass 100 mm. Moist easterly flow over exposed slopes and repeated development along terrain and convergence boundaries could concentrate these higher totals. The placement and persistence of the heaviest cells remain uncertain. Heavy rainfall could produce flooding and localized landslides in steep terrain, with runoff affecting downstream valleys even where local rainfall is lower. Saturday should contribute most of the weekend accumulation. Elsewhere in the Greater Antilles, daytime heating and local convergence will sustain showers and thunderstorms over Cuba, Jamaica, and Puerto Rico. The nearby trough will support instability over Puerto Rico through Saturday, while moisture becomes less consistent Sunday. Lingering moisture over eastern Cuba and Jamaica will support locally heavy convection. Across the Lesser Antilles, passing trade-wind showers will prevail, with increasing moisture favoring the southern Windward Islands later in the period. The monsoon trough and moist Pacific inflow will continue to support convection along Pacific Central America. Upslope flow will favor locally heavy rainfall over Costa Rica and Panama Today and Saturday. Farther northwest, low-level convergence and developing cyclonic flow offshore will favor renewed convection from Pacific Nicaragua toward El Salvador and Guatemala during the weekend, with terrain and repeated storms determining the heaviest accumulations. Across northwestern South America, moist Pacific flow converging along western Colombia and rising over the coastal terrain will sustain locally heavy showers and thunderstorms, particularly Today and Saturday. Over northern Colombia and Venezuela, afternoon heating and local convergence will remain the main triggers for convection, with available moisture controlling its coverage. Tropical Waves Initialized at 12 UTC: TYPE SOF INIT 03/00 03/12 04/00 04/12 05/00 05/12 06/00 06/12 TW 15N 38W 41W 44W 48W 52W 55W 57W 60W 62W TW 17N 69W 71W 74W 77W 79W 81W 83W 85W 87W Alamo...(WPC) $$