Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
991 FXCA62 TJSJ 102006 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 406 PM AST Mon Jun 10 2024 .SYNOPSIS... Warm conditions will persist through tomorrow, and it`s crucial to note that an Excessive Heat Watch will be in effect across all coastal areas of Puerto Rico and the US Virgin Islands. This watch is a significant indicator of potentially dangerous heat levels, urging residents, tourists, and businesses to stay informed and take necessary precautions. By Wednesday, a tropical wave will move over the Caribbean Waters, increasing moisture content and the potential for showers and warmer conditions. Tranquil marine conditions should prevail for the next five days, with seas up to 4 feet and a low risk of rip currents. && .SHORT TERM...Tonight through Wednesday As yesterday, another melting day was observed across the tropical islands. The mid-level rise continued to provide stable weather conditions across the islands under the warmer trend, with minimal rainfall activity across the northwestern side of Puerto Rico. According to some unofficial stations across the islands, heat index values reached 111F in the northwestern quadrant and between 105F and 110F in the north-central areas of Puerto Rico. According to the official climate site at the Luis Munoz Marin Airport in Carolina, the maximum temperature reached 91F. The short-term forecast remains on track. Stable weather conditions will prevail, resulting in the mid-level ridge that continues to hold across the region. Meanwhile, at the surface, a broad area of high pressure extending from the eastern to the central Atlantic will result in east-southeasterly winds over the CWA. Under this wind pattern, the islands will continue to experience a warmer trend, with heat indices between 100F and 112F across all coastal areas and urban sections. Given the expected conditions for tomorrow, an excessive heat watch is in effect for all coastal areas for all the islands. Remember, the heat watch/advisory and warning might not be in effect for some interior municipalities; however, heat indices resulting in heat exhaustion are possible, especially over San Sebastian, Lares, Sabana Grande, and areas near Caguas. Similar surface conditions will hold from Tuesday to Wednesday with the east-southeasterly wind, the broad ridge, and some tropical moisture from a distant tropical wave passing over the Caribbean Waters. However, at the upper levels, a weak upper-level trough will sink southwestward, bringing the northwestern side of the forecast area. Conditions will become slightly favorable for upper cloudiness and some increase in showers over the western sections. Having said that, no widespread shower activity is expected, so the forecast calls for localized showers in the afternoon over the western interior. .LONG TERM...Thursday through Monday...from previous discussion at 436 AM AST Mon Jun 10 2024... Current model guidance suggests normal to below normal Precipitable Water (PWAT) values as a tropical wave will be southwest of the area to start the period. However, an area of normal to above normal PWAT will start to approach the islands from the northeast increasing PWAT values through Friday. This is due to the remnants of a past frontal boundary being pushed towards the area by a high pressure system over the Atlantic. High pressure aloft will also strengthen over the Western Caribbean through the period. Winds through Friday are forecast to be more east to east northeasterly, which could bring some slight relief in terms of warm temperatures although model guidance continues to suggest above normal 925 mb temperatures. Winds are forecast, however, to become more southeasterly by the weekend and through the rest of the period. This will help promote warm temperatures once again. PWAT values return to normal for the weekend with another plume of moisture with above normal to normal values possibly reaching the area by next week. Most available moisture will remain below 850 mb, with only a slight increase in moisture through the mid-levels for the weekend. Saharan dust particles will linger to start the forecast period. && .AVIATION... VFR conditions are expected at all TAF sites during the next 24 hours. At least through 10/22Z, afternoon VCSH/SHRA may briefly impact operations across TJBQ. E-ESE winds at 10-15 knots, becoming at 10 knots or less overnight. && .MARINE... A mid to upper level ridge is promoting generally stable conditions across the local waters. Surface high pressure extending from the northeastern to central Atlantic and north of the area will continue to promote up to moderate to fresh east-southeasterly winds through midweek. A tropical wave is expected to increase the potential for showers and isolated thunderstorms mainly across the Caribbean waters and local passages on Wednesday. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Excessive Heat Warning until 6 PM AST this evening for PRZ001>003-005-007-008-010-011. Excessive Heat Watch from Tuesday morning through Tuesday afternoon for PRZ001>003-005-007-008-010>013. Heat Advisory until 6 PM AST this evening for PRZ012-013. VI...Excessive Heat Watch from Tuesday morning through Tuesday afternoon for VIZ001-002. Heat Advisory until 6 PM AST this evening for VIZ001-002. AM...None. && $$ SHORT TERM...LIS AVIATION...OMS PUBLIC...MMC