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Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
836 FXCA62 TJSJ 150049 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 849 PM AST Wed Aug 14 2024 .UPDATE... Rainfall over portions of the interior and central Puerto Rico continued during the evening hours. Rainfall totals across these areas were between 6 and 10 inches. Runoff from this excessive rainfall and any additional shower activity over Puerto Rico will cause rivers and streams to remain elevated through the night and lead to flash floods. Mudslides are also expected in areas of steep terrain where soils are saturated. Several major rivers and tributaries are still above flood stage across western and north central Puerto Rico. Therefore, a Flash Flood Watch remains in effect for mainland PR through the rest of the overnight and early morning hours. Across the USVI, Vieques and Culebra, the threat for any significant rainfall has diminished and the Flash Flood Watch was cancelled. && ...Corrected Tropical Storm Ernesto to Hurricane Ernesto in previous discussion.... .PREV DISCUSSION... /issued 402 PM AST Wed Aug 14 2024/ SYNOPSIS...At 2 PM AST Hurricane Ernesto was 225 miles northwest of San Juan and moving northwest at 16 mph. The tail of Ernesto is pulling across western Puerto Rico and our western Atlantic waters with scattered showers elsewhere. Some thunderstorms linger. Conditions will improve but southerly flow will cause excessive heat into the weekend. Moisture will return to normal or slightly above normal levels beginning on Friday. SHORT TERM...Tonight through Friday... Hurricane Ernesto will continue to be the dominant influence on the weather through Thursday. The tail of Ernesto will pull across western Puerto Rico and the local western Atlantic waters this evening, but the GFS shows moisture retreating with the storm to the north northwest except for isolated convection later tonight and Thursday. Moisture at 850 mb drops off rapidly tonight and at higher levels on Thursday. Considerable drying will be seen on Friday up through 300 mb. As the convergence into Ernesto moves with the storm to the northwest, a ridge from the surface to 700 mb will move in over the area to reinforce drying and subsidence. This will also greatly decrease the amount of rainfall expected Thursday and Friday. At upper levels a very weak ridge of high pressure will develop over and just north of the area between TS Ernesto and another low pressure currently negatively tilted over 52 west longitude to our east. LONG TERM...Saturday through Thursday... A surface high ridging over the area and the northeastern Caribbean on Saturday will shift northwest into the Bahama Islands by Monday from a quasi stationary high over the Azores. An easterly wave near 35 west on Saturday will move toward the area to about 55 west on Tuesday. At this time it is not carrying a significant amount of additional moisture and will travel well south of Puerto Rico. Better moisture will move into the area behind a weaker wave closely following that will bring showers to the area. Since precipitable water values will continue during the long-term period in the range of 1.4 to 2.0 inches and flow will be mostly southeast over the weekend and turning more easterly during the week, a more typical weather patter will prevail for Puerto Rico and the U.S. Virgin Islands with bands of better moisture even if excessive heat persists early in the period. This will mean early morning showers in eastern Puerto Rico followed by afternoon showers and thunderstorms in western and interior parts of the island. For the U.S. Virgin Islands only isolated to scattered showers are expected with limited amounts of rainfall occurring. Some lines of convection are likely during this period extending with the flow to the west northwest or west of Culebra, Vieques and the U.S. Virgin Islands. AVIATION... (18z) IFR/MVFR conditions are forecast to prevail across TJBQ until at least 14/21z as the rainbands from Hurricane Ernesto move out. For the rest of the PR TAF sites, mainly VFR conds, at times MVFR, will prevail with brief SHRA/TSRA and low CIG thru 14/22z, while USVI TAF sites can expect mostly VFR conds with VCSH. Mostly VFR conds for all TAF sites aft 15/00Z. Winds will remain mainly from the S-SE up to 15 knots and gusty winds up to 28 kts, a more SE wind flow is forecast at around 15/03Z. MARINE...Hazardous seas will slowly retreat with Hurricane Ernesto and small craft advisories are not expected after Thursday at 6 PM AST through Thursday of next week. Nevertheless subsiding swell from Ernesto will continue to arrive in the local area now through Tuesday. Showers and thunderstorms will continue-- especially in the northern waters--through Thursday also with diminishing frequency. BEACH FORECAST...Rip current risk will remain moderate to high over all beaches tonight and moderate on Thursday. Due to the swell returning from TC Ernesto, the rip current risk over the weekend will remain moderate on some northern beaches on Friday. HYDROLOGY...Many rivers across Puerto Rico are in flood stage and some in western Puerto Rico will rise further. The Flash Flood watch has been extended through 8 AM AST. All rivers, if they have not done so by now, should crest soon or overnight. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Flood Watch until 8 AM AST Thursday for PRZ001>011. High Rip Current Risk until 6 AM AST Thursday for PRZ003-008-012- 013. VI...None. AM...Small Craft Advisory until 6 AM AST Thursday for AMZ711-712-741- 742. Small Craft Advisory until midnight AST tonight for AMZ716-723- 726-733-735. && $$ DSR