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) $$