Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
136 FXCA62 TJSJ 292000 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 400 PM AST Wed May 29 2024 .SYNOPSIS... Moisture content is expected to remain normal to above normal, enhancing the potential for afternoon convective activity across northwest Puerto Rico through at least Thursday. A tropical wave is expected to approach the region by Thursday, however, the bulk of moisture should remain over the Caribbean waters. Drier air is expected to filter into the area by the end of the workweek, accompanied by Saharan dust particles. && .SHORT TERM...Tonight through Friday... During the morning hours, light showers filtered over the eastern half of Puerto Rico, leaving less than an inch of rain. The typical afternoon convection developed over the western interior and northwestern sections of Puerto Rico, where the concentrations ranged above an inch of rain. Nonetheless, the intensity of the rainfall and thunderstorm activity was not as strong as in previous days. Overall, seasonal weather conditions prevailed with the east-southeasterly wind flow. Temperature-wise, they remained in the upper 80s to low 90s along the coastal and urban areas, while over the higher elevations, they stayed in the upper 70s to low 80s. Heat indices today stayed below 111 degrees Fahrenheit across Puerto Rico and the U.S. Virgin Islands, staying within the thresholds for Heat Advisory criteria. Tonight, expect variably cloudy skies to prevail across Puerto Rico and the U.S. Virgin Islands as patches of moisture move across the area from time to time. The overnight temperatures should stay in the upper 60s to low 70s across higher elevations and in the 80s along the coastal areas. Wind-wise, they should stay generally light and variable, influenced by land breezes. The latest model guidance continues to suggest the precipitable water content staying around normal to above normal levels through Thursday when a tropical wave moves across the Caribbean waters. The increase in moisture associated with the proximity of the wave will aid in the development of showers and thunderstorms across the region. As usual, after the passage of a tropical wave, a mass of drier air with suspended Saharan dust will filter across the region on Friday. Nonetheless, the local effects combined with the available low-level moisture will trigger afternoon showers and isolated thunderstorms once again, particularly across western Puerto Rico. As mentioned in previous discussions, the warm to hot temperatures will continue through the short-term period under moist east to southeasterly winds. Heat indices are expected to range from 104 to 112 degrees Fahrenheit, mainly along the lower elevations of western and northern Puerto Rico and St. Croix. && .LONG TERM...Saturday through Wednesday... //from previous discussion// A surface high pressure in the central Atlantic will promote south southeasterly winds through much of the long-term-period. Plenty of abundant tropical moisture moving into the local area will help to maintain a wet and unstable pattern across the islands. The latest Precipitable Water Content analysis (PWAT) suggest values of 2.3 to 2.5 inches between Sunday through Monday. This is in response of the development of a surface trough west of the region that will enhance the shower and thunderstorm potential across Puerto Rico and the U.S. Virgin Islands. Sufficient moisture in combination with daytime heating and local effects, will lead to convective activity across the central interior and northwestern portions of Puerto Rico during the afternoon hours. Therefore, there is a limited to elevated risk of isolated flash flooding, urban and small stream flooding, river rises, and mudslides. By Tuesday into Wednesday as the surface trough lingers north of the area, moisture from the Caribbean waters will continue to be lifted and moved over the islands. Winds are expected to veer from the south by Tuesday in response to the combination of the surface trough and a approaching tropical wave. With this scenario the potential for moderate to heavy rainfall and isolated thunderstorms remains high. Despite the anticipated weather scenario, warmer to hot temperatures are expected each day. Daytime temperatures are expected to reach the upper 80s to low 90s. Meanwhile, overnight temperatures will remain in the upper 70s to low 80s along the coastal and urban areas of the islands. Heat indices may reach the mid to upper 100s during the period, especially during the mid-morning to early afternoon hours. && .AVIATION... (18z TAFs) Aftn convection will remain psbl mainly across the ctrl Mtn range of PR and downwind from the USVI til 29/23Z. SHRA/VCTS with ocnly gusts btwn 15-25kt psbl at TJBQ and vcty til 29/23z. SFC wnds mainly fm E at 15 kt or less with sea breeze variations, bcmg calm to lgt/vrb aft 29/23Z. Expect E winds at 10-15 kt with sea breeze variations and ocnly hir gusts aft 30/14Z. && .MARINE... A moderate east to southeast wind flow will prevail across the region over the next few days. The next tropical wave will move into the Eastern Caribbean later tonight, moving far to the south of Puerto Rico and the U.S. Virgin Islands between early Thursday and early Friday. && .BEACH FORECAST... There is a moderate risk of rip currents across the northwestern beaches of Puerto Rico, and the beaches of St. Croix. Elsewhere, there is a low risk. Moderate to heavy showers and isolated thunderstorms are possible each afternoon mainly across the northwestern waters of Puerto Rico. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...MMC/RAM LONG TERM....GRS AVIATION...RAM PUBLIC DESK...RVT