Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
807 FXCA62 TJSJ 192134 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 534 PM AST Wed Jun 19 2024 .SYNOPSIS... For the latter half of the workweek, winds are forecast to back and become more easterly and increase in speed. Columnar moisture will remain at normal to above normal. Afternoon shower and thunderstorm activity should concentrate more on interior to western PR and downwind of the local islands. More seasonal conditions are expected this weekend, but still with enough moisture to generate showers and isolated thunderstorms. Hot conditions will persist each afternoon, with little relief for areas with the lowest cloud coverage. && .SHORT TERM...Tonight through Friday... Afternoon shower and thunderstorm activity was observed across most of the area with the strongest activity over western and northern municipalities. These showers and thunderstorms were fast moving, finally moving offshore and or dissipating. The highest rainfall amounts were reported around Manati, Barceloneta and Arecibo, peaking at around 4.18 inches in Barceloneta. High heat indices above 106 degrees were reported in several coastal areas, before generalized afternoon convection and cloudiness was able to provide relief in that aspect to most areas. Precipitable water (PWAT) values are above normal (above 2.0 inches) over the region. Current model guidance has the bulk of PWAT leaving the area during the overnight hours. For Thursday and Friday, columnar moisture will remain normal to above normal as as patches of moisture move across the region. The interaction between a broad surface high over the Central Atlantic and an induced surface trough northwest of the local islands has promoted southeasterly winds today. For tonight, remnant afternoon showers will continue lingering and gradually dissipating while showers and possible thunderstorms move towards the eastern and southern coastal areas from the waters. As we head into the second half of the weekend the surface trough will move westward and the surface high will build, due to this winds are forecast to back and become more easterly while increasing to moderate and locally fresh speeds. Under these easterly winds and patches of moisture, afternoon shower and thunderstorm activity should concentrate more on interior to western PR and downwind of the local islands. Lows tonight up to upper 70s and around 80 across lower elevation areas. 925 mb temperatures should remain at normal to above normal values. .LONG TERM...Saturday through Wednesday... ./FROM PREV DISCUSSION...Issued at 349 AM AST Wed Jun 19 2024/ A surface high pressure centered over the eastern Atlantic will drive the trade winds from the east during the weekend, bringing occasional showers across eastern Puerto Rico and the Virgin Islands, and followed by afternoon convection across western Puerto Rico. Early next week, a mid level ridge will build north of the region, and the surface high pressure will strengthen as it moves westward. At this time, an induced surface trough will approach the area, and a tropical wave will cross the eastern Caribbean. The moisture from these surface features will bring an increase in showers to the area, mainly for the Virgin Islands, local waters and eastern Puerto Rico. Accumulations are not expected to be too significant because the low level steering flow will be enhanced. Saharan dust will follow on Tuesday, lasting through Wednesday. Then on Wednesday, another trough will dig from the northeast, shifting the winds from this direction. All these days, afternoon convection is anticipated, mainly for the interior and western Puerto Rico. The activity could be strong, with possible lightning, and urban and small stream flooding developing. The heat risk will be elevated all these days, impacting outdoor activities, and those without effective cooling or poorly hydrated. && .AVIATION... (18Z TAFS) Tempo MVFR conds are possible at TJBQ/TJSJ thru 19/23z, and mostly VCSH elsewhere during the overnight hours. Otherwise, VFR conds expected to prevail thru 20/15z. TSRA developing once again aft 20/16z across central and western PR, causing VCTS at TJBQ/TJPS. ESE winds up to 15 kt will prevail in general across all terminals, with land breeze variations during the night. HZ due to Saharan dust but VSBY should remain P6SM. && .MARINE... Surface high pressure over the Atlantic will promote moderate to locally fresh easterly winds through the rest of the week. Passing showers and isolated thunderstorms accompanying and trailing a tropical wave will continue to affect the coastal waters and local passages resulting in localized hazardous marine conditions. && .BEACH FORECAST... For tonight, there is a moderate risk of rip currents for St. Croix and eastern Vieques. For tomorrow, the moderate risk of rip currents will spread to Culebra as well as to the northern, southwestern and southeastern coastline of Puerto Rico. For tomorrow night, the moderate risk of rip currents will spread to the northern USVI. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM....CAM LONG TERM.....MRR PUBLIC DESK...YZR