Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
848 FXCA62 TJSJ 280859 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 459 AM AST Fri Jun 28 2024 .SYNOPSIS... The primary concern for the short-term period will continue to be heat, at least through this weekend. Additionally, some suspended Saharan dust particulate is expected by tomorrow and will persist through early next week, contributing to hazy skies and a moderate to localized high heat risk. Afternoon convection is likely every day, mostly over western Puerto Rico. Invest 95L will start to impact the local area from late Monday night through Tuesday as it moves south over the Caribbean waters. Continue to monitor the forecast as this event unfolds. && .SHORT TERM...Today through Sunday... Trade wind showers increased overnight across the regional waters and over portions of the islands. The Doppler radar estimated around a tenth of an inch in St. John and half an inch over northeastern Puerto Rico. Minimum temperatures were from the upper 60s to mid 70s across the higher elevations, and from the upper 70s to low 80s across coastal municipalities. Winds were light from the east to northeast. A gradual increase in moisture content is expected through Saturday. Today, a trade wind perturbation will continue to induce scattered showers across the local waters and enhance afternoon shower and thunderstorm activity mainly across the interior and western sections of Puerto Rico. A northeasterly component in the winds in combination with the sea breeze convergence and daytime heating will favor showers over the SW quadrant of PR. Urban and small stream flooding is expected with this activity. It will be hot again across the islands and a Heat Advisory (NPWSJU) was issued for St. Croix, and for the north, south, and western coastal counties of Puerto Rico. Maximum temperatures should reach the low 90s across the lower elevations with heat indices ranging between 108F-112F before the onset of afternoon convection. A wind shift from the east to southeast is expected on Saturday as a tropical wave moves across the eastern Caribbean. Shower activity will increase in coverage as well as thunderstorms across the local waters. Urban and small stream flooding will remain as the main weather hazard, particularly across the NW quadrant of PR on Saturday afternoon. Trailing the wave there is a Saharan Air Layer with moderate amounts of Saharan dust that should cause hazy skies across the USVI by Saturday evening, spreading across the rest of the area through Sunday. Therefore, a decrease in shower activity is expected on Sunday in general. However, afternoon convection will still develop over western PR. .LONG TERM...Monday through Friday... By early next week, drier air will filter across the islands, with suspended Saharan dust particulate engulfing the area. This will promote hazy skies and limit the potential for shower activity throughout most of the day. Although isolated to localized scattered showers cannot be ruled out, particularly during the afternoon hours, excessive heat threat will continue as southeasterly winds prevail, advecting warm temperatures across the northeastern Caribbean and combining with the Saharan Air Layer. The rest of the long-term forecast continues to appear active. A tropical wave (Invest 95L or AL95) located several hundred miles west-southwest of the Cabo Verde Islands is being monitored by the National Hurricane Center (NHC), with a high potential of developing into a tropical depression or tropical storm in the next day or so. However, model guidance suggests that this system will stay south of the local islands, crossing the Caribbean Sea by late Monday night through Tuesday. Despite the expected system remaining over the Caribbean waters, the broad moisture field will engulf the forecast area, increasing the potential for squally weather. Therefore, as AL95 approaches, expect increased cloudiness and deteriorating conditions with heavy showers and gusty winds. A limited to elevated flooding threat can be anticipated, particularly as it interacts with the Cordillera Central in Puerto Rico. Another tropical wave behind AL95, centered a few hundred miles south-southwest of the Cabo Verde Islands, is also being monitored by the NHC. Although significant development of this system is not anticipated at the moment. Model guidance suggests this tropical wave will also move south of the islands. Similarly, although a direct impact is not anticipated, the moisture field will again cover the forecast area, maintaining wet and unstable weather conditions from Thursday through the end of the workweek. Forecast confidence is low to moderate regarding the impact of both tropical waves on the forecast area by next week. Therefore, continue to monitor the forecast, as slight deviations in the tracks of AL95 and the tropical wave behind it could change the expected impacts across the local islands. && .AVIATION... (06Z TAFS) Mainly VFR conditions are expected to prevail across all terminals during the next 24 hours. However, SHRA/TSRA expected to develop over the interior of PR, which may cause MVFR conds in and around TJPS/TJSJ/TJBQ btw 28/17z-22z. Across the USVI terminals, mostly VCSH with brief periods of -SHRA can be expected. E-ENE winds at 12- 16 kt with stronger gusts and sea breeze variations aft 28/14z. && .MARINE... A surface high pressure over the central Atlantic will promote light to moderate east-southeasterly winds. Trade wind showers will move across the regional waters from time to time due to a tropical wave moving south over the Caribbean Waters by Saturday. Another tropical wave with a high potential of developing into a tropical cyclone, according to the National Hurricane Center, will move into the Caribbean Sea by late Monday night into Tuesday, likely deteriorating marine conditions. && .BEACH FORECAST... There is moderate risk for the island of St. Croix. Elsewhere, the risk is low. Deteriorating conditions is expected by early next week, particularly across south-facing beaches as Invest 95L approaches and moves south of the area across the Caribbean Sea. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for PRZ001-003-005-007-008-010-011. VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for VIZ002. AM...None. && $$ SHORT TERM/AVIATION...DSR LONG TERM/MARINE/BEACH....CVB