textproduct: San Juan

KEY MESSAGES

Issued at 256 PM AST Sun Jul 5 2026

* Moderate to locally high concentrations of Saharan dust will affect the islands through the middle of the week. Expect hazy skies, reduced visibility, and deteriorating air quality.

* Elevated heat risk is expected each day. Hot temperatures combined with the available moisture will increase the risk of heat-related illnesses, particularly for those spending prolonged periods outdoors or without adequate cooling.

* A moderate risk of rip currents will continue at several local beaches through the middle of next week. Life-threatening rip currents are possible. Swim near a lifeguard, heed beach warning flags, and follow the advice of local beach patrols.

* A tropical wave may increase the risk of heavy rainfall, thunderstorms, and localized flooding by the middle of next week. Forecast confidence will improve over the coming days. Continue to monitor the latest forecast updates.

Short Term(This evening through Tuesday)

Issued at 256 PM AST Sun Jul 5 2026

Today we had a mix of clouds at low, mid, and upper levels, resulting in partly to mostly cloudy skies at times. Local network measurements showed moderate to high concentrations of suspended particles today, which is forecast to diminish slowly. We noted warmer-than-normal morning temperatures today, with afternoon temperatures climbing into the upper 80s and lower 90s, producing peak heat indices around 100F. East to east-southeast winds ranged from 10 to 20 mph with higher gusts and local sea-breeze variations. Showers developed near the Luquillo Mountain Range (across the El Yunque Rainforest) early this afternoon.

The air quality will continue to deteriorate due to the Saharan Air Layer, promoting hazy skies, reduced visibility, and generally suppressing widespread rainfall across Puerto Rico and the U.S. Virgin Islands. Temperatures will remain above normal, especially across urban and coastal areas.

Daytime heating, local factors, and the moisture available will likely contribute to another day of localized showers in the interior and western sections of Puerto Rico, as well as in areas downwind of the U.S. Virgin Islands.

Derived satellite imagery also indicated an increasing trend in Total Precipitable Water (TPW), remaining within normal July values, and this trend will continue to increase slowly by Monday and Tuesday. Although limited rainfall is anticipated, we still expect daytime heating, local effects, and available moisture to support locally induced convection across the interior and western sections of Puerto Rico, as well as downwind of the U.S. Virgin Islands each day. The Galvez-Davison Index (GDI) suggested afternoon thunderstorms across western and interior PR daily.

The islands will experience a warm-to-hot weather pattern through the short term, particularly from mid-morning to the afternoon, when Heat Advisories may be issued.

Long Term(Wednesday through Sunday)

Issued at 352 AM AST Sun Jul 5 2026

The long-term remains on track, though the flooding threat may extend into Thursday. As mentioned in the previous discussion, the wind pattern should remain mostly from the E-ESE, as a surface high pressure builds north of the CWA and maintains breezy to windy conditions across the islands. The latest model guidance continues to suggest a well-defined tropical wave approaching the Caribbean Basin and moving across the CWA on Wednesday, along with a wind surge. This system should pool tropical moisture into the region, with low- and mid-level RH peaking around 80%, well above the climatological normal. Additionally, Grand Ensemble members (including GEFS and ENS) continue to tend to wetter conditions, with PWAT values reaching 2.0 - 2.2 inches. As mentioned in the previous discussion, model guidance suggests cooler than normal mid-level temperatures (500 mb between -8 and -9 degrees Celsius), enhanced vertical motion, and vorticity, indicating favorable conditions for deep convection. In addition, GDI values remain high on Wednesday, particularly over the regional waters and portions of eastern and northwestern Puerto Rico. Hence, the discussed scenario prevails, with showers and isolated thunderstorms moving into windward sections of Puerto Rico and the U.S. Virgin Islands during the morning, followed by afternoon convection over interior and northwestern Puerto Rico. Due to strengthening winds, daytime heating, and local effects, local streamers could develop and move over portions of eastern Puerto Rico, including the San Juan Metropolitan Area. Rainfall accumulations could result in ponding of water over roadways and poorly drained areas, along with urban and small stream flooding over the aforementioned areas, with low flash flood chance over northwestern Puerto Rico. Although the latest NASA/GMAO Dust AOT suggests low concentrations of SAL that may linger across the local area on Wednesday, this could enhance rather than limit lightning activity, particularly during afternoon convection.

In the previous discussion, model guidance suggested a drier air mass filtering into the region by Thursday, though the latest global solutions suggest an abundance of moisture content over the CWA, associated with another tropical wave approaching the Caribbean basin. Although the area of enhanced convection should remain well south of the region, lingering moisture associated to the system combined with daytime heating and local effects may result in afternoon convection, once again, across western/northwestern Puerto Rico, with the San Juan streamer as well. Although periods of heavy rainfall can be expected, theres uncertainty regarding the arrival of the tropical wave and the SAL. For the rest of the forecast period, the dense plume of Saharan Dust should persist and limit shower activity, with isolated showers moving from time to time.

The latest model guidance suggests seasonal 925 mb temperatures, slightly near above climatological normal. Nevertheless, the combination of available moisture and winds with a southerly component will likely trigger heat indices to reach 100 degrees Fahrenheit across urban and coastal areas of the islands. In addition, the dense plume of Saharan Dust will likely inhibit nighttime cooling, with warmer minimum temperatures. Hence, the heat threat will remain elevated throughout the forecast period.

AVIATION

(18Z TAFS) Issued at 256 PM AST Sun Jul 5 2026

VFR conditions will persist along the forecast TAF sites during the period. The presence of Saharan dust particles will continue to result in HZ lowering the VIS across the area. SOme VCSH to -SHRA are forecast for TJSJ from now to 05/21Z. Winds will persist from the E- SE until 05/23Z and peaking again at 06/12Z up to 18 knots and gusty winds.

MARINE

Issued at 256 PM AST Sun Jul 5 2026

A high-pressure system over the central Atlantic will promote moderate to fresh east to east-southeast winds and choppy seas across the region through the middle of the week. A tropical wave will cross the Lesser Antilles between late Tuesday night and early Wednesday morning, crossing the local islands around Wednesday morning, which could increase the chance of thunderstorms. A dense Saharan Air Layer will continue to spread across the region, lowering visibility and, at times, worsening air quality.

BEACH FORECAST

Issued at 256 PM AST Sun Jul 5 2026

Increasing easterly winds will continue creating hazardous beach conditions across portions of Puerto Rico and the U.S. Virgin Islands. A moderate risk of life-threatening rip currents will persist at several local beaches and expand to additional beaches through early next week as winds strengthen and breaking wave action increases. Even at beaches with a low risk, isolated life- threatening rip currents remain possible, especially near jetties, groins, reefs, and piers.

Expect hot and humid conditions at the beaches each afternoon, with dangerous heat levels possible. Isolated thunderstorms may also develop over western Puerto Rico. Remember: When thunder roars, go indoors. Stay hydrated, seek shade frequently, wear lightweight clothing, and limit prolonged sun exposure during the hottest part of the day.

FIRE WEATHER

Issued at 256 PM AST Sun Jul 5 2026

Elevated fire weather conditions will persist across portions of Puerto Rico as dry fuels, low relative humidity, and breezy conditions continue. Fine fuels remain critically dry across southern Puerto Rico following several weeks of limited rainfall, while afternoon relative humidity values in the upper 40s to mid-50s and easterly winds of 15 to 20 mph, with higher gusts, will continue to support rapid fire spread.

Although elevated fire danger will persist, sudden dangerous conditions could occur, particularly across southern and southwestern Puerto Rico, where fuels remain driest. Residents and visitors should exercise extreme caution with fireworks, grills, and any activity involving open flames, as even a small spark could quickly ignite dry vegetation and lead to a fast-moving wildfire.

SJU WATCHES/WARNINGS/ADVISORIES

PR...None. VI...None. AM...None.