988 FXCA62 TJSJ 291320 AFDSJU Area Forecast Discussion National Weather Service San Juan PR Issued by National Weather Service Miami FL 920 AM AST Fri Sep 29 2017 .UPDATE... Made some minor tweaks to the forecast mainly Sky/Pop/Temp. Rain chances will increase beginning late morning. Short range models develop scattered showers and storms in the next few hours with locally heavy rainfall possible. Flash Flood Watch and Rip Current Statement look good. Updates sent. && .PREV DISCUSSION... /issued Issued by National Weather Service Miami FL/ AVIATION... For the 12Z TAFs....Showers and thunderstorms are expected to increase in coverage through the morning and afternoon hours. Predominate VFR will give way to tempo MVFR as convection develops and impacts the terminals. Light to moderate east winds will be the rule, perhaps gusty in and around convection. Indications are that convection will last into the evening hours across VI and towards the end of the TAF period invading PR. PREV DISCUSSION... /issued Issued by National Weather Service Miami FL/ .PERIODS OF HEAVY RAINFALL MAY CAUSE FLASH FLOODING ACROSS PUERTO RICO AND THE U.S. VIRGIN ISLANDS... SHORT TERM... Current satellite imagery shows an upper-level low moving slowly westward across the northern Caribbean Sea with a large plume of tropical moisture surging northward across the Leeward Islands this morning. Radar imagery from the northern islands showed convection earlier from Antigua to St. Kitts, but they have mostly died out since. As mid-level winds turn southeasterly this morning, deep moisture will overspread the U.S. Virgin Islands and Puerto Rico through the evening with precipitation chances quickly increasing throughout the day and into Saturday. Locally heavy rainfall is expected and additional flash flooding is possible, which would hinder recovery efforts. A Flash Flood Watch continues for the entire forecast area. See the Hydrology section for additional information and potential impacts. There is a high risk of rip currents through Friday along the northern Atlantic coastline of Puerto Rico and St. Croix with a moderate risk on the southern coast. The Rip Current Statement will continue through Friday afternoon due to dangerous northerly swells continuing. LONG TERM... As the upper-level low continues westward away from Puerto Rico, deep tropical moisture will remain in place through Monday, keeping the chance of showers and thunderstorms in the forecast. Though the best forcing will be associated with the upper low this weekend, locally heavy rainfall potential will continue through early next week, but there is lower confidence on amounts at this point. The rest of the week, modest moisture from the surface to around 700mb will warrant generally 30 to 40% PoPs each day. Light surface winds will turn to the ESE/SE Thursday and Friday, putting the best moisture convergence in the western/interior portions of Puerto Rico and in the higher terrain. Temperatures will be near or below normal through much of the forecast period with expected cloud cover and precipitation chances. AVIATION... Moisture will increase substantially Friday morning through the afternoon with showers and thunderstorms expected to increase in coverage across much of the area. Have kept VFR conditions prevailing across the western areas on this package but MVFR or lower ceilings will certainly be possible, especially across the eastern and interior portions of Puerto Rico and the U.S. Virgin Islands with periods of heavy rainfall also possible. HYDROLOGY... Deep tropical moisture will overspread the islands this morning from east to west and continuing this weekend. Rainfall amounts of 2 to 4 inches with locally higher amounts are likely each day with precipitable water values nearing or exceeding 2.00". Soils are already saturated and most of the rivers and small streams are running above or well above normal levels, therefore there is a high risk of river and small stream flooding as well as mudslides in areas of steep terrain. Urban flooding is also likely across low-lying areas as well as poor drainage areas where water pumps are not working at full capacity. A FLASH FLOOD WATCH has been issued for all islands beginning Friday morning. MARINE... Moderate easterly winds and seas will dominate across the area through the weekend. Northerly swells continue to push into the northern sections of the islands where small craft will need to exercise caution. Showers and thunderstorms will become numerous beginning Friday with winds and seas locally higher in and around stronger convection. && .PRELIMINARY POINT TEMPS/POPS... SJU 83 79 82 80 / 70 40 70 50 STT 82 80 81 80 / 70 50 70 50 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through Saturday morning for Mayaguez and Vicinity-North Central-Northeast-Northwest-San Juan and Vicinity-Southeast-Western Interior. Flash Flood Watch through late Sunday night for Central Interior- Culebra-Eastern Interior-Mayaguez and Vicinity-North Central-Northeast-Northwest-Ponce and Vicinity-San Juan and Vicinity-Southeast-Southwest-Vieques-Western Interior. VI...High Rip Current Risk through Saturday morning for St Croix. Flash Flood Watch through late Sunday night for St Croix- St.Thomas...St. John...and Adjacent Islands. AM...Flash Flood Watch through late Sunday night for Coastal Waters OF Southwestern Puerto Rico out 10 NM-Coastal Waters of Northern USVI and Culebra out 10 NM-Coastal Waters of Southern Puerto Rico out 10 NM-Coastal Waters of Southern USVI Vieques and Eastern Puerto Rico out 10 NM. && $$ SHORT TERM...99 LONG TERM....99