Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
266 FXCA62 TJSJ 182116 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 516 PM AST Tue Jun 18 2024 .SYNOPSIS... Unstable weather conditions will continue through at least late tomorrow across the islands. An upper trough and area of low pressure continue to become amplified west of the region through tomorrow. This along with a tropical wave will maintain moist and unstable conditions through mid week resulting in periods of developing showers and isolated thunderstorms each day. Winds will remain from the southeast before gradually backing to become easterly tomorrow and further increasing on Thursday. Current model guidance has the entire region with PWAT values above 2 inches tomorrow, with remnant moisture patches reaching the area on Thursday. A slight to moderate concentration of Saharan dust is forecast to spread across the area tomorrow into Thursday. && .SHORT TERM...Tonight through Thursday... Afternoon convection started over western and northwestern quadrant Puerto Rico as strong thunderstorms started to develop. As these thunderstorms gradually moved offshore, another cluster developed over interior to north-central Puerto Rico moving northeast and offshore before reaching Guaynabo. Pea-size hail was reported between 2:45 and 255 PM in Corozal due to these thunderstorms. Thunderstorm wind damage was also reported in Morovis as gusts damaged plantain trees and displaced some trash collecting drones. The highest rainfall amounts (around 2.6 inches) were reported in the border of Mayaguez, Las Marias and Maricao. High heat indices above 106 degrees were reported in several coastal areas. Unstable weather conditions will continue through at least late tomorrow across the islands. A surface high pressure system over the Central Atlantic and an induced surface trough northwest of the region are promoting light southeast surface winds across the islands. Winds will remain from the southeast before gradually backing to become easterly tomorrow and further increasing on Thursday. Current satellite derived precipitable water (PWAT) values show normal (mainly over southern PR and the Caribbean Waters) to above normal values over most of the region. PWAT values will continue above normal tomorrow as a tropical wave and abundant moisture behind it is also near the area. Current model guidance has the entire region with PWAT values above 2 inches tomorrow, with remnant moisture patches reaching the area on Thursday. An upper trough and low pressure continue to become amplified west of the islands through tomorrow. For tonight, remnant afternoon showers will continue lingering and gradually dissipate while showers and possible thunderstorms move towards the eastern region and coastal southern PR. Shower and thunderstorm activity tomorrow can concentrate over eastern PR, the metro area, and interior to western and northwestern Puerto Rico, mainly during the afternoon hours. 500 mb temperatures will be normal to above normal (colder temperatures) and increasing mid level moisture and relative humidity will be present tomorrow. Convective activity on Thursday will focus more on interior to western PR under easterly winds. due to the easterly winds across the area. A slight to moderate saharan air layer is also forecast to reach the area during the period. .LONG TERM...Friday through Tuesday... ./FROM PREV DISCUSSION...Issued at 445 AM AST Tue Jun 18 2024/ Conditions are so far forecast to improve by Friday with increasing stability aloft, as the previously mentioned upper trough west of the area weakens and high pressure builds across the area from the central and eastern Caribbean. Low level moisture transport will also erode as the easterly winds increase resulting in less frequent passing late evening and early morning shower activity. The potential for afternoon shower development and isolated thunderstorms will continue on Friday but mainly due to local effects and good daytime heating. Shower activity should be more localized and focused over the interior and west section of Puerto Rico steered by the moderate trade winds. Overall improving condtions is expected elsewhere on Friday and into Saturday with plenty of sunshine and near seasonal temperatures expected. For the rest of the following weekend prevailing easterly winds are forecast with periods of passing early morning showers affecting the windward side of the islands. This will be followed by afternoon convection limited to mainly parts of the central interior and west sections of Puerto Rico. Plenty of sunshine and mostly pleasant summertime weather is expected elsewhere although a weakly induced easterly perturbation will cross the region late Saturday into Sunday followed by the next topical wave so far forecast to enter the eastern Caribbean late Sunday then cross the region Monday through Tuesday. That said expect lesser showers and thunderstorm activity across during the early part of the period with the best potential for increasing instability and convection so far forecast for the latter part of the period on Monday and Tuesday due to the approaching tropical wave and associated moisture field. && .AVIATION... (18Z TAFS) Brief periods of MVFR conditions will remain possible at JSJ and JBQ in TSRA/SHRA through at least 18/22z. Aft 18/22z VFR conditions will prevail at all TAF sites with VCSH/VCTS. Winds are 10-15 kts from the E-SE, and more VRB after 18/22z. The chance for SHRA/TSRA will increase tomorrow with a tropical wave passage. && .MARINE... Surface high pressure over the Atlantic and a tropical wave crossing the region will promote light east to southeast winds today, then becoming more easterly and increasing to moderate to locally fresh by Wednesday and through the rest of the week. Passing showers and isolated thunderstorms accompanying and trailing the tropical wave will continue to affect the coastal waters and local passages resulting in localized hazardous marine conditions. && .BEACH FORECAST... There is a low risk of rip currents for all coastal areas tonight. A moderate risk of rip currents will be present by tomorrow morning for St. Croix and then by tomorrow night for Vieques and sectors of eastern Puerto Rico. The moderate risk of rip currents will then likely spread to Culebra, SW Puerto Rico, SE Puerto Rico and northern Puerto Rico on Thursday. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM....CAM LONG TERM.....MRR PUBLIC DESK...YZR