Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
690 FXCA62 TJSJ 200820 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 420 AM AST Thu Jun 20 2024 .SYNOPSIS... 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. A wet pattern will continue into next week as moist air lingers across the region from the arrival of tropical waves. && .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...Sunday through Thursday... A surface high stretched across the central Atlantic will bring a pattern of trade wind showers followed by afternoon convection across the islands on Sunday into the early of next week. Plenty of moisture remains over the area with consistent high precipitable water values which will yield in an abundance of showers at times. By Tuesday, a tropical wave begins to move across the area, bringing unstable conditions across the the lower levels and continuing the trend of moist conditions. Generally relatively high pressure will remain across the mid to upper-levels during this time, however with the instability caused by the tropical wave and a continued east to southeasterly flow, rain may be persistent and heavy a few time throughout this period. Afternoon convection due to local effects and diurnal heating will play a big role in allowing thunderstorms to form, with western Puerto Rico most likely to receive the bulk of rain and the greatest risk of excessive rainfall. && .AVIATION... (06Z) Mainly VFR conditions expected to prevail. SHRA will move at times across the waters, and after 17Z, will form in the western half of the Cordillera Central, causing mountain obscuration. Winds will increase today, out of the east at 15-20 kts, with gusts up to 25 knots, mostly from 14-22Z. && .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 associated with a tropical wave will continue to affect the coastal waters and local passages resulting in localized hazardous marine conditions. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...ERG LONG TERM...RC