314 FXCA62 TJSJ 190851 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 451 AM AST Sat Jul 19 2025 .KEY MESSAGES... * Another hot day for the US Virgin Islands and Puerto Rico today, before the formation of intense thunderstorms during the afternoon and evening of Saturday, which could lead to flooding rains. * The trailing moisture from today`s surface trough will bring another round of thunderstorms on Sunday afternoon. * The excessive heat trend is expected to persist throughout much of the forecast period, particularly between Tuesday and Thursday. * If model guidance follows the correct track, a robust tropical wave could bring a wet and unstable weather pattern around next Friday. && .SHORT TERM...Today through Monday... Satellite and radar imagery showed partly cloudy skies and isolated showers during the overnight period across the local waters, with some showers reaching the northern and eastern coasts of Puerto Rico and the U.S. Virgin Islands (USVI). Radar estimates did not indicate significant rainfall accumulations. Temperatures ranged from the upper 60s in the mountains to the upper 70s and low 80s in coastal urban areas. Winds were mainly from the northeast at 10 mph or less. The short-term forecast remains on track. Today, a TUTT low moving north of the region will induce a surface trough that will pass near the islands, enhancing afternoon convection and increasing the potential for thunderstorms. Model guidance suggests that precipitable water (PWAT) values will remain between 1.7 and 1.9 inches. Winds will shift from the northeast to the east-southeast throughout the day. As a result, expect showers across windward locations during the morning, followed by an active and unstable afternoon with showers and isolated to possibly scattered thunderstorms over interior and northwestern Puerto Rico, as indicated by the Galvez Davison Index (GDI). The USVI also has a good chance of experiencing occasional periods of showery weather throughout the day. There is an elevated risk of ponding of water on roads and in poorly drained areas, as well as localized flooding in urban zones, roadways, and small streams. In addition, a period of warm to hot heat indices is expected to persist. Although showers and thunderstorms may help reduce the heat risk, high humidity will contribute to muggy conditions in urban and coastal areas of Puerto Rico, especially before rain develops or in places that receive limited rainfall. As a result, a Heat Advisory is in effect between 10 a.m. and 4 p.m. AST for coastal urban areas of Puerto Rico. Looking ahead to Sunday and Monday, expect a more typical summer pattern for the tropics, with morning showers across the eastern half of Puerto Rico and the USVI, followed by afternoon convection mainly confined to the northwestern quadrant of Puerto Rico. Rainfall should be more localized, and the flood risk will be limited. However, warm to hot temperatures will continue. Residents and visitors are encouraged to stay hydrated, limit outdoor activity during peak heat hours, wear light clothing, and check on vulnerable individuals and pets. .LONG TERM...Tuesday through Saturday... A mid-level high pressure will build over the northeast Caribbean from Tuesday into next weekend, promoting dry air aloft, at least through Friday. While a surface high-pressure will persist across the Atlantic Ocean, promoting an increase in local winds from around Wednesday into the end of the workweek. A weak easterly perturbation is expected to move across the islands around Tuesday, enhancing the potential for rain and thunderstorm activity, especially during the afternoon hours. After Tuesday`s easterly disturbance, the local weather will be dominated by the arrival of patches of moisture embedded in the trades, which will promote the climatological hydrological pattern of the US Virgin Islands and Puerto Rico on Wednesday and Thursday. Based on the latest model guidance during this period, the primary hazard could be excessive heat resulting from the combination of available moisture and maximum temperatures across the islands. A tropical wave, which currently appears to be the primary rain and thunderstorm producer, is expected to arrive around Friday, and its trailing moisture could persist near the region through at least next Saturday, potentially pausing the excessive heat trend. We are monitoring this wave, as it could increase the potential to observe flooding rain, especially around Friday, for both PR and the USVI. Additionally, NHC is currently monitoring this same wave in their Tropical Weather Outlook for the Atlantic waters, and it has a low chance of formation over the next 7 days. && .AVIATION... (06Z TAFs) Mostly VFR conds across all terminals and VCSH across eastern TAF sites during the morning hours. Intermittent MVFR conditions possible over TJBQ (SHRA/VCTS) starting around 19/17Z. Winds from the ENE veering to ESE today at around 10 to 15 kts with higher gusts after 19/13Z. Lighter and variable tonight. && .MARINE... An induced surface trough will bring an increase in showers and thunderstorms across the regional waters today into early Sunday morning. A surface high pressure over the Atlantic will mainly promote moderate easterly winds over several days, becoming moderate to fresh again around Tuesday next week. Another weak easterly perturbation will arrive around Tuesday. && .BEACH FORECAST... Beachgoers can expect a low risk of rip currents for most local beaches in Puerto Rico and the US Virgin Islands through at least Tuesday. Regardless of the low risk, isolated stronger rip currents may occur, especially near piers, jetties, and channels. Thunderstorms will develop from around noon into the evening, increasing the risk of lightning strikes along the coastal locations today. Please monitor our social media platforms for further updates. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>005-007- 008-010-011. VI...None. AM...None. && $$ SHORT TERM...YZR LONG TERM....CAM AVIATION...YZR
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