SHORT TERM
Tonight through Sunday...

Satellite and radar observations have indicated predominantly partly cloudy to cloudy skies across the region throughout the day. With the residual moisture from the departing tropical wave and the proximity of a mid to upper-level trough north of the islands, periods of showers and thunderstorms have persisted, mainly across the eastern local waters, St Thomas, and northern, eastern, and southeastern sectors of Puerto Rico. Approximately 1.0 to 2.0 inches of rainfall fell in those areas at the moment and rain is ongoing. A Flash Flood Warning was issued for St Thomas and Flood Advisories were issued for eastern PR. It was another day with warm to hot temperatures. Surface observations showed mid to upper 80s in higher elevations and peaked in the lower to mid 90s across lower and coastal areas of Puerto Rico and the USVI islands. The Heat Advisory is still in effect until 5 PM AST for northern, western, and southern PR and St Croix as heat indices are exceeding the 100s.

At this time, rain activity is mainly over the local waters, eastern areas, and northwestern Puerto Rico and should continue at least for the next one, two hours or so.

For tonight, a change in the pattern is anticipated. Moisture will gradually diminish as a drier air mass arrives with precipitable water values around near-normal to below-normal values (between 1.4 and 1.8 inches), resulting in more stable conditions. This mass will be accompanied by a moderate to severe Saharan Air Layer and warmer-than-normal temperatures maintaining a dry and hazy weather pattern through at least Saturday, however some afternoon and evening convection cannot be ruled out of the forecast, particularly over western Puerto Rico and the surrounding waters, but accumulations should not be too impressive. We encourage residents and visitors to stay hydrated and limit sun exposure for prolonged periods as additional Heat Advisories or Warnings may be needed. On Sunday, some moisture arrives with the wind flow increasing the potential for showers during the day.

LONG TERM
Monday through Friday...

PREV DISCUSSION
/issued 435 AM AST Fri Jul 5 2024/

On Monday, residual Saharan dust particles will remain in low concentrations across Puerto Rico and the U.S. Virgin Islands.
Nonetheless, by late Monday, expect an increase in moisture and shower activity as a tropical wave, along with a wind surge, reaches the islands on Tuesday. Precipitable water models show values in the 50th percentile or around normal climatological levels for this time of the year with the passage of this tropical wave. This wave will move relatively fast across the region, particularly on Tuesday. With it, expect the passing showers to increase across the islands during the morning hours, with moderate to heavy showers and isolated thunderstorms expected across the western and northwestern portions of Puerto Rico during the afternoon hours. Trailing moisture associated with the tropical wave will prevail over the long-term period.

The latest model guidance continues to suggest a strong surface to mid-level high-pressure system over the central Atlantic. This weather feature will maintain the wind flow out of the east- southeast through at least Friday. With these weather conditions, we anticipate warm weather conditions with temperatures in the 90s along the coastal and urban areas of the islands and in the upper 70s to low 80s in the mountainous areas. As mentioned in previous discussions, the mixture of warm temperatures and the available moisture will result in higher heat indices across the region, surpassing the mid-100s.

AVIATION

(18Z TAFS)

SHRA and isolated TSRA will persist across the Atlantic waters promoting MVFR/IFR or worse for TIST/TJSJ at least through 05/20z.
HZ due to Saharan dust will increase, with VSBY dropping to 6SM at times. Winds will be light and variable aft 05/23z, but will rise once again after 06/14z mainly from the SE, shifting more ESE at 10- 15KT with higher gusts, but there will be sea breeze variations.

MARINE

Residual moisture from a departing tropical wave will continue to bring showers and thunderstorms across the regional waters for the next hours before a drier airmass with Saharan Dust arrives. A strengthening surface high pressure over the central Atlantic will extend into the northeast Caribbean through the weekend, leading to moderate to fresh easterly winds. The next tropical wave will be approaching the islands by late Monday night into Tuesday, increasing the chance of showers across the local waters.

BEACH FORECAST

Tonight, the rip current risk should remain moderate along the southern beaches of Puerto Rico, Vieques, and Saint Croix, elsewhere should remain low. Similar conditions are expected tomorrow. For additional information, consult the Surf Zone Forecast (SRFSJU)
issued by the NWS San Juan Office.

SJU WATCHES/WARNINGS/ADVISORIES
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001-003-005- 007-008-010-011.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ002.

AM...None.