Mona Passage Southward to 17N Marine Forecast
| Rest Of Today...Northeast Winds 10 To 15 Knots With Gusts Up To 25 Knots. Seas 3 To 4 Feet, Occasionally To 5 Feet. Wave Detail: Northeast 4 Feet At 6 Seconds. Scattered Showers Late This Morning, Then Isolated Showers Early This Afternoon. Scattered Showers With Isolated Thunderstorms Late. |
| Tonight...Northeast Winds 15 To 20 Knots With Gusts Up To 30 Knots. Seas 4 To 6 Feet, Occasionally To 8 Feet. Wave Detail: Northeast 5 Feet At 6 Seconds. Scattered Showers In The Evening. |
| Sunday...Northeast Winds 15 To 20 Knots, Increasing To 20 To 25 Knots In The Afternoon. Seas 5 To 7 Feet, Occasionally To 9 Feet. Wave Detail: Northeast 6 Feet At 8 Seconds. |
| Sunday Night...Northeast Winds 20 To 25 Knots With Gusts Up To 30 Knots. Seas 5 To 7 Feet, Occasionally To 9 Feet. Wave Detail: Northeast 7 Feet At 8 Seconds. Scattered Showers In The Evening. |
| Monday...North Winds 15 To 20 Knots With Gusts Up To 25 Knots. Seas 5 To 7 Feet, Occasionally To 9 Feet. Wave Detail: North 6 Feet At 9 Seconds. |
| Monday Night...North Winds 15 To 20 Knots, Becoming Northeast 10 To 15 Knots After Midnight. Seas 5 To 7 Feet, Occasionally To 9 Feet. Wave Detail: North 6 Feet At 9 Seconds. Scattered Showers. |
| Tuesday...Northeast Winds 5 To 10 Knots. Seas 4 To 6 Feet, Occasionally To 8 Feet. Scattered Showers In The Morning. |
| Tuesday Night...Northeast Winds 5 To 10 Knots. Seas 4 To 6 Feet, Occasionally To 8 Feet. Scattered Showers. |
| Wednesday...Northeast Winds 5 To 10 Knots. Seas 3 To 5 Feet, Occasionally To 6 Feet. Scattered Showers In The Afternoon. |
| Wednesday Night...East Winds 5 To 10 Knots. Seas 3 To 4 Feet, Occasionally To 5 Feet. Scattered Showers. Winds And Seas Higher In And Near Thunderstorms. |
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Area Forecast Discussion National Weather Service San Juan PR 529am AST Sat April 19 2025 Synopsis The combination of a mid-to-upper-level trough and surface- induced trough, as well as available moisture, will continue to promote a moist and unstable pattern during this weekend. Therefore, periods of strong showers with thunderstorms will promote an elevated potential for urban flooding and minor small- stream flooding. Marine and coastal conditions will also deteriorate with a Small Craft Advisory starting this evening for the offshore Atlantic waters, and a High Risk of Rip Currents starting tomorrow for the north-oriented beaches of Puerto Rico. .SHORT TERM...Today through Monday... Radar and satellite data indicated an increase in shower activity overnight, driven by low-level moisture convergence under northeasterly trade winds. The most active areas included the northern and eastern half of Puerto Rico, Culebra, and the northern U.S. Virgin Islands. Since 8pm AST, radar estimates suggest peak rainfall totals of about half an inch across portions of north- central and far eastern Puerto Rico. Temperatures overnight ranged from around 60°F in the higher elevations of the Cordillera Central to the mid-70s across eastern Puerto Rico and the U.S. Virgin Islands. Winds were generally from the north to northeast at 5–15 mph along windward areas, while remaining light and variable across southern and interior sections. A mid-to-upper-level trough, in combination with a surface-induced trough, will continue to dominate the regional weather pattern, fostering a persistently unstable and moist atmosphere favorable for deep convective development through Sunday and sustaining the potential for increased showers and thunderstorms. The environment will feature a weak or nearly absent trade wind cap inversion, promoting vertical cloud growth. At the same time, mid-level temperatures will remain unusually cool—with 500 mb values dipping to around -10°C between today and Saturday—further enhancing instability. This setup, combined with persistent low-level moisture convergence, will support efficient rainfall processes, with precipitable water values ranging from 1.8 to 2.0 inches, well above normal for this time of year. A significant transition in the weather pattern is anticipated by late Sunday into Monday. A drier air mass will quickly filter into the region, accompanied by increasing convergence and subsidence aloft, associated with the trough's trailing side. This will lead to less favorable conditions for deep convection and promote a more stable atmosphere. As a result, a notable decrease in shower and thunderstorm activity is expected to start the new workweek. Given the current setup, there is an elevated risk of flooding, particularly in areas that experience persistent or repeated rounds of convection through late tonight. Urban locations, poor drainage areas, and regions with already saturated soils are especially vulnerable. Localized flash flooding cannot be ruled out. Additional hazards include lightning strikes and strong thunderstorm winds. For more information on potential weather hazards, refer to the Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=sju. Long Term Tuesday through Saturday... Current model guidance has precipitable water values (PWAT) at 1 to 1.20 inches to start the long term period, gradually increasing as we continue into the period. To start the period, a mid to upper level trough will be northeast of the islands, gradually deteriorating as we head in to the midweek. A surface trough, however, will continue to cross the region, promoting east- northeasterly steering flow on Tuesday, gradually backing to become southeasterly by Wednesday. An more east-southeast Thursday and into the weekend. A notable increase in PWAT (Precipitable Water) values is forecast by late Thursday, with most of the region having more than 1.5 inches of PWAT, with the eastern region having around 2.0 inches. By late Saturday, current model guidance has most of the region at around 2.0 inches (above normal values for this time of the year). Most available moisture will be confined to below 700 mb through at least late Friday. In general, weather conditions are forecast to gradually improve during the start of the next workweek, overnight and morning showers are still forecast over windward areas while afternoon convection will still occur over sectors of western PR, with exact locations depending on the prevalent steering flow that day. The increase in moisture to end the workweek and into the next weekend can increase the coverage of this activity. 925 mb temperatures are forecast to be at below to normal values to start the period, gradually climbing due to east-southeast flow during the second half of the workweek. Marine A surface high pressure system over the western Atlantic will continue to push remnant showers of a past frontal boundary across the region over the next few days while a nearby mid to upper level trough and a surface trough produces favorable conditions for their development. This will lead to increased showers and thunderstorms across the local waters. Increasing northeasterly winds and a weak northerly swell will deteriorate marine conditions by this evening and into early next week. A Small Craft Advisory is in effect for the offshore Atlantic Waters. Beach Forecast A low to (in some areas of north-central and northwestern PR) moderate risk of rip currents is expected today. Tonight, the risk increases to moderate for all north-oriented beaches of Puerto Rico. Life-threatening rip currents often occur in the vicinity of groins, jetties, reefs, and piers. For tomorrow, Sunday, increasing winds and a weak northerly swell will further deteriorate coastal conditions. A High Risk of Rip Currents is forecast for the north-oriented beaches of Puerto Rico, from Rincon to Fajardo, through at least early Tuesday. A High Risk of Rip Currents means that life-threatening rip currents are likely in the surf zone. If you become caught in a rip current, yell for help. Remain calm, do not exhaust yourself and stay afloat while waiting for help. If you have to swim out of a rip current, swim parallel to shore and back toward the beach when possible. Do not attempt to swim directly against a rip current as you will tire quickly. Beachgoers should also remain vigilant for afternoon thunderstorms, especially along the western and southwestern coasts of Puerto Rico this weekend, where dangerous lightning may occur. .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk from Sunday morning through late Monday night for PRZ001-002-005-008-010. VI...None. AM...Small Craft Advisory from 6pm this evening to 6am AST Tuesday for AMZ711. |
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