Marine Weather Net

Puerto Rico and US Virgin Islands from 10NM to 19.5N Marine Forecast


5 - 10


10 - 15


10 - 15


10 - 15

The Marine Weather Forecast In Detail:
AMZ710 Forecast Issued: 929 AM AST Wed Mar 08 2023

Rest Of Today...West Winds 5 To 10 Knots. Seas 3 To 5 Feet With Occasional Seas Up To 6 Feet. Dominant Period 10 Seconds. Isolated Showers.
Tonight...Northwest Winds 10 To 15 Knots, Becoming West After Midnight. Seas 3 To 5 Feet With Occasional Seas Up To 6 Feet. Dominant Period 10 Seconds. Isolated Showers.
Thursday...Northwest Winds 10 To 15 Knots. Gusts Up To 25 Knots In The Afternoon. Seas 4 To 6 Feet With Occasional Seas Up To 8 Feet, Building To 6 To 8 Feet With Occasional Seas Up To 10 Feet. Dominant Period 11 Seconds. Numerous Showers.
Thursday Night...North Winds 10 To 15 Knots. Gusts Up To 25 Knots In The Evening. Seas 8 To 10 Feet With Occasional Seas Up To 11 Feet. Dominant Period 11 Seconds. Isolated Showers.
Friday...North Winds 10 To 15 Knots, Becoming Northeast. Seas 6 To 8 Feet With Occasional Seas Up To 10 Feet. Dominant Period 11 Seconds. Isolated Showers.
Saturday...East Winds 5 To 10 Knots, Becoming South. Seas 8 To 10 Feet With Occasional Seas Up To 11 Feet. Dominant Period 12 Seconds. Isolated Showers.
Sunday...Southwest Winds 5 To 10 Knots, Becoming East. Seas 6 To 8 Feet With Occasional Seas Up To 10 Feet. Dominant Period 14 Seconds.
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Area Forecast Discussion
National Weather Service San Juan PR
529pm AST Wednesday July 17 2024

Favorable conditions aloft and above-normal moisture levels will maintain the potential for showers and isolated thunderstorms early tonight. However, a drier-than-normal airmass and a dense Saharan dust spreading across the northeastern Caribbean will bring more stable weather and hazy skies by Thursday. By Friday and into the weekend, a passing tropical wave will increase the likelihood of showers and isolated thunderstorms, raising flooding concerns. Despite the expected increase in cloud cover and high rain chances, warm-to-hot conditions will persist.

.SHORT TERM...Tonight through Friday... Satellite and radar observations have indicated predominantly sunny to partly cloudy and hazy skies throughout the region, with occasional showers affecting eastern Puerto Rico and afternoon convective development over northwestern Puerto Rico. Daytime high temperatures varied significantly, peaking in the lower 80s in higher elevations and climbing to the mid-90s in lower elevations. Meanwhile, heat index values soared above 108-112 degrees, especially in the lower elevations of northwestern to north- central Puerto Rico, where
Excessive Heat Warning...nd Advisories were in effect. In the U.S. Virgin Islands, daytime highs ranged around 88 to 94 degrees, with heat indices in the mid 100s. Winds were generally from the east to east-southeast, with stronger gusts and sea breeze effects leading to 15-25 mph speeds. Wind gusts in the 30-40 mph range were reported across northeastern Puerto Rico, Culebra, and the northern U.S. Virgin Islands.

The short-term forecast period features several key elements: a series of TUTT lows and surface-induced features, a Saharan Air Layer (SAL), and a tropical wave. Instability generated by a TUTT low to the north and above-normal moisture levels across the region will maintain the potential for showers and isolated thunderstorms tonight. The highest risk is expected for eastern Puerto Rico and the local islands, where these storms may bring heavy downpours, frequent lightning, and gusty winds. As a result, there are excessive rainfall risks or flooding concerns, with potential impacts ranging from water ponding on roads, poorly drained areas, and urban and small stream flooding. Residents and visitors are advised to stay updated on weather conditions.

By late tonight and continuing through the workweek, a dense SAL will cause a moderate to severe dust event, worsening health conditions for immunocompromised individuals, vulnerable populations, and those sensitive to air quality issues. This event will also result in hazier skies and reduced visibility. Along with an expected drier-than-normal airmass, with precipitable water values dropping near or below seasonal thresholds, expect a gradual decrease in convective development by Thursday. Dust concentrations are expected to decrease by Friday with the arrival of a tropical wave and its associated moisture field, supporting an increase in showers with thunderstorm activity.

Warmer-than-usual conditions will persist in the coming days. Coastal and urban areas can expect nighttime lows in the lower 80s, while higher elevations will see temperatures drop to around 70 degrees. Daytime highs will range from the lower 90s in lower elevations to around 80 degrees in higher elevations. With abundant moisture in the air, heat indices in many coastal and urban regions may soar above 108 degrees Fahrenheit. These conditions present significant health risks, requiring the issuance of Excessive Heat Advisories and Warnings. It is crucial for residents and visitors, especially those participating in outdoor activities, to take necessary precautions to stay safe.

Long Term
Saturday through Thursday... From previous discussion issued at 513am AST Wednesday July 17 2024

Strong surface high pressure will remain the dominant feature across the Atlantic and north of the region. This will maintain moderate east to northeast winds through Saturday as a tropical wave and associated moisture field enters the eastern Caribbean and crosses the forecast area. This increasing moisture will bring unstable conditions to the region followed by a wind surge and moderate to strong southeasterly winds by Saturday afternoon and early Sunday as the tropical wave exits the region. Trailing the wave an extensive layer of dense Saharan dust will quickly spread across the region the rest of the weekend and linger through Monday then diminish from Tuesday onwards. Low level winds are then expected to become more easterly as another Tutt and induced surface trough is forecast to approach the region from the east. All in all Hot, humid and hazy conditions will likely be the dominant weather pattern through the weekend and into the early part of the following week with some locally and diurnally induced afternoon convection each day.

Recent model guidance continued to initialize well and suggests the most impactful period to be Friday through Saturday due to increasing moisture convergence and instability. That said there will be a better chance for enhanced overnight and afternoon convection as the tropical wave and somewhat cooler advective temperatures aloft are across the region. As previously mentioned considerably hazy conditions and fairly drier airmass will follow due to the dense layer of Saharan dust particulates. Local temperatures will remain slightly above normal with maximum daytime heat indices forecast to be elevated to significant at times especially along the coastal and urban areas. Marine conditions area also forecast to deteriorate through the weekend due to the tightening of the local pressure gradient and a wind surge which will increase the tradewinds. Precautionary statements and or small craft advisories may therefore continue for portions of the local waters and passages due to the choppy wind driven conditions.

Sunday through Monday are forecast to be the driest period with typical summertime weather and hot and hazy conditions. Isolated to scattered locally and diurnally afternoon convection expected mainly over the west and northwest sections of Puerto Rico. By late Monday through the rest of the period, the upper ridge will erode as a Tutt low is forecast to retrograde across the region and low level moisture gradually increases. This will again increase the chance for more frequent overnight passing showers followed by afternoon convection across parts of the islands.

Based on the Tropical Weather Outlook from the National Hurricane Center...Tropical cyclone formation is not expected during the next seven days.

Strong surface high pressure anchored across the west central Atlantic will yield moderate to locally fresh easterly winds. Consequently, choppy to hazardous seas for small craft are likely across the local waters and passages. Precautionary statements will continue and Small Craft Advisories have been issued for portions of the local waters, beginning Thursday night. Showers with isolated thunderstorms are expected to affect the local waters from time-to-time.

Beach Forecast
For the remainder of the week, there will be a moderate risk of rip current for most beaches and therefore life-threatening rip currents will be possible in the surf zone.

.SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...Small Craft Advisory from midnight Thursday night to midnight AST Friday night for AMZ711-723.