Tropical Discussion - International Desks NWS Weather Prediction Center College Park MD 1231 PM EDT Thu Mar 13 2025 Forecast Bulletin 13 March 2025 at 1630 UTC: ...Caribbean Basin... Over the next several days, the upper levels are showing signs of fast progressing upper troughs that will favor the presence of a frontal boundary that will extend from the central Atlantic and reach the Greater Antilles and remain stationary. The current negative phase North Atlantic Oscillation (NAO) is potentially assisting with the presence of a frontal boundary as far south as Hispaniola and Puerto Rico during this time. Model guidance is suggesting that the conditions of the negative NAO phase are expected to continue over the next several days and could begin changing until the next work week. The upper level troughs will have short wave troughs embedded that will propagate south into the central Atlantic by Friday, affecting the frontal boundary over the Greater Antilles. The presence of a prefrontal trough over Puerto Rico on Friday will enhance convection over the island and the increase in precipitable water will favor moderate precipitation. By Saturday, the upper trough continues towards the east and away from the North Caribbean, weakening the frontal boundary over the Greater Antilles and thus decreasing precipitation. The rest of the Caribbean Basin will see the presence of moist plumes that are propagating in the easterly trades. Significant precipitation totals are not expected elsewhere. In terms of precipitation, on Thursday, expect maxima of 20-35mm in the Dominican Republic, while south Haiti, Jamaica, and Puerto Rico/VI can expect maxima below 25mm. On Friday, Puerto Rico/VI can expect maxima of 25-50mm, while the Dominican Republic can expect maxima of 20-35mm. South Haiti, Jamaica, and the south Windward islands can expect generalized maxima of 15-20mm. On Saturday, Puerto Rico/VI can expect maxima of 20-35mm, while Jamaica, south Hispaniola, and the Lesser Antilles can expect maxima of 15mm. ...Mexico and Central America... The majority of the region is governed by a potent mid to upper level ridge that is favoring subsidence and dry conditions over the majority of the region from central Mexico through south Central America. The exception is northwest Mexico, where a fast moving upper trough and accompanying frontal boundary enters the Baja California Peninsula by Thursday evening. Favoring moist onshore flow into the region, enhancing lift due to the terrain, and favoring moderate totals of 20-40mm in north Baja California, and maxima of 10mm in south Baja California and north Sonora on Thursday. The cold front is extends from the southwest United States into north Sonora, exiting into the Pacific Ocean through north Baja California Sur. By Friday evening, the frontal boundary has quickly progressed trough the central United States and enters east Coahuila. Minimal precipitation is expected as the amount of available moisture remains low. By Saturday evening, the cold front extends from Alabama/Louisiana-United States and enters north Veracruz as it becomes stationary along the northern Sierra Madre Oriental. Similar to Friday, the amount of available moisture remains low and a potential for localized showers is expected in Veracruz. To the south in Central America, available moisture remains low and isolated showers are expected in regions such as the Golfo de Fonseca region and along the south-central region of Costa Rica due to the presence of low level troughs and some moisture. However, significant precipitation totals are not expected and maxima should remain below 15mm/day. ...Tropical South America... The intensifying Bolivian High in central South America will begin to meander over the region and interact with other upper level systems in north South America favoring areas of diffluence, especially over northwest South America. These interactions will provide the ventilation for deep convection as low level troughs are propagating over the Amazon River Basin over the next three days and reach the northern Andes mountains in Colombia and Peru by Saturday. In west Colombia and Ecuador, moist onshore flow is expected to enter the region from the southwest, favoring convection over the next three days. Due to the diffluence present in the upper levels over Colombia and Ecuador, localized higher amounts could be anticipated in western Colombia and Ecuador. In terms of precipitation, on Thursday, expect maxima of 35-70mm in western Ecuador, and maxima of 25-50mm in west Colombia, Amazonas-Brasil, and from north Guyana into east Venezuela. Maxima of 20-45mm are expected from the Amazon Delta into the eastern Amazon Basin, and a maxima of 20-35mm from north Peru into east Ecuador. On Friday, expect maxima of 35-70mm from south-central Colombia into east Ecuador, and maxima of 25-50mm from south Venezuela into the central Amazon River Basin. Maxima of 20-45mm are expected from Suriname to Amapa-Brasil, and maxima of 20-35mm are expected in west Colombia and Ecuador, and from south Colombia into north Peru. On Saturday, expect maxima of 40-80mm from central Colombia into north Peru and east Ecuador. Maxima of 30-60mm are expected from south Venezuela to the Central Amazon Basin, while west Colombia into northwest Ecuador can expect maxima of 25-50mm. The Amazon Delta can expect maxima of 20-45mm while maxima of 20-35mm are expected from Canaima-Venezuela into east Amazonas-Brasil. For a graphical representation and details of the areas with forecast rainfall: https://www.wpc.ncep.noaa.gov/international/crb_day1-3.shtml Castellanos...(WPC)