textproduct: San Juan

KEY MESSAGES

* A departing perturbation will result in passing showers this morning, followed by afternoon convection over the interior and western to southwestern Puerto Rico.

* A tropical wave combined with an upper-level trough, will increase the frequency of showers and thunderstorms particularly Wednesday and Thursday. As a result, the risk of flooding will remain elevated.

* The Virgin Islands will also experience an increase in showers and thunderstorms, potentially leading to water surges in drainage guts, ponding on roadways, occasional lightning, and isolated landslides.

* A Heat Advisory is in effect today across coastal and urban areas of Puerto Rico, as well as Vieques, Culebra and the Virgin Islands. Increasing heat risk is forecast again toward the end of the week and into the weekend.

* There is a moderate risk of rip currents across the northern and eastern beaches of Puerto Rico, as well as Culebra and St. Croix today. A low risk is expected in other areas.

LONG TERM...Friday through Tuesday

For Friday and Saturday, the upper-level trough will weaken, allowing a weak mid-level high pressure to slightly dominate. The latest model guidance suggests that precipitable water (PWAT) values will remain within the normal range for this time of year, ranging from 2.0 inches on Friday and decreasing to 1.5 inches by Saturday. Expect afternoon showers and isolated thunderstorms fueled by diurnal heating and local effects. As a result, urban and small stream flooding is likely to persist each day, and some rivers may reach flood stage. In the Virgin Islands, periods of showers and thunderstorms are expected to cause water surges along guts and drainage channels, ponding on roadways, and isolated urban flooding. Additional hazards include landslides, frequent lightning, and gusty winds.

This forecast scenario assumes that the current guidance remains consistent regarding the tropical wave being monitored by the National Hurricane Center, which currently has an 80% chance of formation in the next 48 hours and a 90% chance over the next seven days. If development continues as expected, the system may track northwestward toward the northeastern Caribbean. We will continue to monitor this closely and provide updates throughout the workweek.

Sunday through Tuesday should be the more stable days of the forecast period, with 500 mb temperatures warming to above normal, around -5 to -4 degrees Celsius. Drier air is forecast to move into the region, with below normal PWAT values persisting through Tuesday (1.5 inches or lower). Rainfall activity will diminish, but localized afternoon convection, particularly in the western sectors of Puerto Rico, will still be possible due to local effects and diurnal heating. Winds will be very light, so showers will be very slow moving, and the flood risk will remain mostly limited. By Tuesday night, another tropical wave is expected to approach the area, further increasing moisture and bringing better chances for rain onward.

In terms of temperatures, 925 mb values are forecast to peak at nearly two standard deviations above normal from Friday into the weekend. This pattern will elevate the heat risk across the region. Heat Advisories or even Extreme Heat Warnings may be issued. Residents and visitors are strongly advised to stay hydrated, avoid prolonged sun exposure during peak heat hours, and take extra precautions, particularly those without access to adequate cooling or hydration.

AVIATION

(06Z TAFs)

SHRA/TSRA are expected across the region over the next 48 hours, bringing periods of MVFR to brief IFR conditions. Activity will mainly affect TJSJ and USVI terminals through 16/16Z, shifting to TJBQ and TJPS through 16/22Z, then returning to TJSJ and USVI terminals after 16/22Z. Winds will be light to calm and variable early, increasing to 1520 kts with gusts up to 2530 kts between 16/14-22Z, before diminishing again to light and variable after 16/22Z. Gusty winds are possible near SHRA/TSRA.

MARINE

A surface high pressure system located over the central and eastern Atlantic, in combination with a departing low-level perturbation, will promote moderate to locally fresh east to northeasterly winds today. Small craft are urged to exercise caution across the offshore waters and local passages. Passing showers and isolated thunderstorms will continue through the morning hours across most waters, followed by stronger thunderstorms across the western waters of Puerto Rico and the Mona Passage during the early afternoon hours. A stronger tropical wave is expected to approach late tonight into Wednesday, enhancing intensity and shower coverage.

BEACH FORECAST

Today, there is a moderate risk of rip currents across the north and east-facing beaches of Puerto Rico, Culebra, and St. Croix. Similar conditions are expected to prevail most of the workweek so beachgoers are advised to exercise caution at all times as a moderate risk means life-threatherning rip current are possible in the surf zone. A low risk should prevail elsewhere. Additional hazards include afternoon thunderstorms. Remember, if you hear thunder, seek shelter inside of a safer place immediately.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for PRZ001>005-007-008-010>013.

VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for VIZ001-002.

AM...None.