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Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
044 FXCA62 TJSJ 150955 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 555 AM AST Thu Aug 15 2024 .SYNOPSIS... Hurricane Ernesto now located north of 23N, and over 300 miles northwest of San Juan, will maintain moderate southerly wind flow across the area today into Friday as it moves north northwestward and farther away from the region. Overall weather conditions are forecast to gradually improve throughout the day with winds becoming more southeasterly then easterly by Friday and into the weekend. A low to moderate concentration of Saharan dust will arrive and spread across the region later today and into the upcoming weekend along with a weak easterly wave which will arrive across the local area late Friday into Saturday. Overall hot and humid conditions will promote excessive heat conditions for some coastal and urban areas for the next several days. && .SHORT TERM...Today through Saturday... Current Satellite derived precipitable water (PWAT) indicate remnant moisture from the tail of the now far northwest Ernesto maintaining up to 2.0 inches (borderline above normal values for this time of the year) over the region. Rainfall yesterday have kept several rivers under a Flood Advisory overnight, with the last ones, Rio Culebrinas, Rio Grande de Manati and Rio Guanajibo being under a Flood Advisory until early this morning. Light showers have persisted over interior Puerto Rico overnight as southerly flow keeps bringing moisture over the area. Lows ranged from the mid to upper 70s over north-central to northwestern, and eastern interior, PR to the low 80s across most other coastal areas of the islands. Only isolated sectors of interior PR had lows in the upper 60s and low 70s. As Ernesto continues to move further away from the region, moisture across the islands will gradually decrease today to normal PWAT values. PWAT values will remain at normal values, with even drier patches of air arriving at times. Ridging trough at least 700mb will move into the region during the period, promoting more drying and subsidence. Southerly to southeasterly flow will dominate the period. Winds from this direction tend to promote warmer than usual conditions. An increased heat risk will be present today as heat indices elevate to above 108-110 degrees at coastal and lower elevation areas of the islands. Citizens and tourists are encouraged to practice heat safety measures as we end the workweek. Passing showers will affect windward sectors at times with convective activity developing due to diurnal heating, sea breeze convergence and local orographic effects over sectors of the interior and northwest, today and tomorrow. Data from the Puerto Rico Landslide Forecast Network shows high levels of soil saturation. With these saturated soil conditions and lingering moisture during the rest of today and the next few days, any additional shower development across these areas can promote ponding of water on roads and minor flooding as well as mudslides in areas of steep terrain. By the start of the weekend, a weak tropical wave will increase instability and increase PWAT values to normal/above normal values once again. Saharan dust will also be present during the short term period, producing somewhat hazy skies. .LONG TERM...Sunday through Thursday... A surface high building across the area and the northeastern Caribbean will spread further west northwest Across west and southwest Atlantic increasing the easterly trade winds. An tropical wave is forecast to cross the eastern Caribbean Sunday through Monday and will bring a quick surge of moisture and increase passing showers to the region along with another low to moderate concentration of Saharan dust. By then winds are to become more east southeast and thus maintain hot and humid conditions. Better moisture is still forecast to move across the region accompanying another tropical wave by the middle of the following week will bring another surge of additional moisture and increase the potential for enhanced shower activity across the area. Precipitable water values will range between 1.5 to 2.0 inches with a prevailing east to southeast wind flow through the period. Therefore a more typical weather pattern will prevail for Puerto Rico and the U.S. Virgin Islands except for the occasional patches of trade wind moisture forecast to cross the region from time to time accompanying the moderate easterly trades. Therefore periods of passing overnight and early morning showers will persist over the coastal waters and eastern Puerto Rico and the U.S. Virgin Islands, followed by afternoon showers and thunderstorms mainly over western and the interior parts of the island each day. For the U.S. Virgin Islands periods of isolated to scattered showers are expected with limited amounts of rainfall accumulations expected at this time. && .AVIATION... (06Z TAFS) Mainly VFR conditions across the terminals. S-SE winds up to around 15 kts with higher gusts will be present, decreasing after 15/22Z. Afternoon VCSH/Iso-VCTS starting over the interior can affect TJPS around 15/17Z-22Z. Light Saharan dust will also promote somewhat hazy skies. && .MARINE...Hazardous seas will slowly diminish as Hurricane Ernesto pulls farther away from the region. Therefore small craft advisories are not expected after noon today and for the rest of the week. However choppy conditions will continue due to the moderate to locally fresh south to southeast winds. Nevertheless small subsiding swell from Ernesto may continue to arrive across the local Atlantic waters through the upcoming weekend. Showers and isolated thunderstorms will also remain possible over portions of the local waters and passages especially during the late afternoon and evening hours. && .BEACH FORECAST...Rip current risk will remain moderate for all beaches Today. Due to the swell returning from TC Ernesto, the rip current risk will remain moderate for some northern beaches on Friday and through the upcoming weekend. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for PRZ001-002-005-008-010-012-013. VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for VIZ002. AM...Small Craft Advisory until noon AST today for AMZ711-741. && $$ SHORT TERM...MRR LONG TERM....RAM AVIATION...MRR