263 FXCA62 TJSJ 120759 AFDSJUArea Forecast Discussion National Weather Service San Juan PR 359 AM AST Fri Sep 12 2025
.KEY MESSAGES...
* Afternoon showers and thunderstorms are expected for central and western Puerto Rico, due to the abundant moisture and diurnal heating effects.
* For the U.S. Virgin Islands; warm temperatures and mainly fair weather conditions will prevail today, under mostly sunny to partly cloudy skies.
* Hot temperatures will persist during the next several days across the region. A Heat Advisory is in effect from 10 AM to 4 PM AST for the urban and coastal areas of Puerto Rico, Vieques, Culebra, and all of the U.S. Virgin Islands.
* There is a low risk of rip currents for all beaches of the local islands.
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.SHORT TERM...Today through Sunday...
Mostly tranquil conditions were observed during the night hours across the islands. Some showers managed to reach St. John and southeastern Puerto Rico, but accumulations were not significant. Skies were mostly clear, with some high clouds moving in. Temperatures were just a tad cooler than yesterday, but still in the low 80s in the Virgin Islands, and in the 70s in Puerto Rico.
A couple of troughs, one to the northeast, and one well northwest of the islands will maintain the trade winds weaker for today and Saturday. In general, the mornings will be mostly pleasant, with passing showers reaching the Virgin Islands, Vieques and Culebra and eastern Puerto Rico at times, although no significant rainfall accumulation is anticipated. In the afternoon, near normal moisture levels and strong diurnal heating will lead to another active afternoon. Showers and thunderstorms are expected to develop along the Cordillera Central, and with a weak steering flow, these showers will then spread into the west and northwest of Puerto Rico, as well as over portions of the San Juan metro area. Showers could also fire up in the western portions of St. Croix, streaming toward the Caribbean Sea. The highest risk of flooding is for the interior, northwest, and the San Juan metro area, where urban and small stream flooding could develop. Also, frequent lightning and gusty winds are expected within the strongest thunderstorms.
Some drier air is expected early on Sunday, leading to fair weather for most of the northeast Caribbean, but then a tropical wave will approach the Virgin Islands, with a higher chance of showers in the vicinity of Saint Croix in the afternoon hours. The moisture field of the wave will spread westward, also increasing the frequency of showers for the rest of the Virgin Islands and eastern Puerto Rico. Winds will increase too, coming from the east southeast at speeds of 20 to 25 mph.
Temperatures at 925 mb are just a tad cooler than yesterday, but still, well above normal heat indices will prevail. A Heat Advisory is in effect for most of Puerto Rico and all of the Virgin Islands. A Heat Advisory means that people sensible to heat will be affected, especially those without effective cooling or adequate hydration.
.LONG TERM...Monday through Friday...
A tropical wave is forecast to move over Puerto Rico and the U.S. Virgin Islands, bringing increased moisture and a high likelihood of showers and thunderstorms. The latest precipitable water guidance indicates normal to above-normal values (2.00 to 2.25 inches), suggesting a wet pattern will persist through Tuesday. The U.S. Virgin Islands should anticipate showers and isolated thunderstorms, particularly from the morning into the afternoon. In Puerto Rico, showers and isolated thunderstorms are expected over the eastern municipalities during the morning, with afternoon convective activity shifting to the western and northwestern municipalities due to a combination of daytime heating and local effects.
This wet trend is expected to continue from Wednesday through the rest of the week, as an upper-level trough located northeast of the region moves southeast. A second tropical wave approaching the area will combine with the available moisture from the upper-level- trough, further enhancing the potential for additional showers and thunderstorms across the islands. Therefore, the risk of excessive rainfall leading to urban and small stream flooding remains elevated. There is also a limited risk of frequent lightning accompanying the strongest thunderstorms.
Despite the expected weather for the long-term period, the 925 mb temperature is expected to remain above-normal at the beginning of the week. However, as the week progresses, temperatures will become slightly cooler due to the increased rainfall. Highs will generally be in the mid to upper 80s along coastal and urban areas, and in the upper 70s to low 80s in the higher elevations. Residents and visitors are advised to monitor weather conditions and plan any outdoor activities accordingly for the upcoming week.
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.AVIATION... (06Z TAFs)
Mainly VFR conditions expected to prevail. SHRA will move in the vicinity of the USVI terminals, but limited, if any, impacts to operations are expected. After 17Z, another round of strong convection is expected for the Cordillera Central, reaching TJSJ and TJBQ at times. Periods of reduced VIS and low ceilings are expected as well. Winds will be lighter, out of the ESE at 7-11 kts.
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.MARINE...
A surface high pressure across the central Atlantic and a front over the western Atlantic will promote light to moderate east to southeast winds through the weekend. Afternoon showers and thunderstorms are likely each day, particularly over the northwestern coastal waters of Puerto Rico and over the Mona Passage.
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.BEACH FORECAST...
A low risk of rip currents is expected to continue through the weekend. However, even with a low risk, life- threatening rip currents can still occur near groins, jetties, reefs, and piers, so beachgoers are advised to exercise caution at all times. The rip current risk is forecast to increase to moderate again by early next week. Additional hazards include: isolated afternoon thunderstorms and an elevated to significant heat risk. Remember: if you hear thunder, seek shelter indoors immediately, and be sure to stay well hydrated.
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.SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon for PRZ001>005-007-008-010>013.
VI...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon for VIZ001-002.
AM...None. &&
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SHORT TERM/AVIATION...ERG LONG TERM....GRS
NWS SJU Office Area Forecast Discussion