This Saturday will go from extreme heat to an afternoon with possible showers and isolated thunderstorms

The weather pattern this Saturday will go from extreme heat in the morning to an active afternoon of rain and with the possibility of developing isolated thunderstorms over some sectors, especially in the west-northwest region.

This scenario will be possible due to the combination of excess heat, for which there are warnings issued for several towns, with the humidity that will be brought by a weak tropical wave that passes through the local area today.

Below are the details of the weather forecast for this Saturday:

• He National Weather Service (SNM) in San Juan issued a extreme heat warning to Arecibo, Barceloneta, Dorado, Florida, Manati, Vega Alta, Vega Baja, Aguadilla, Camuy, Hatillo, Isabela, Quebradillas, Aguada, Anasco, Hormigueros, Mayaguez, Moca, Rincon, San German, Cabo Rojo, Guanica, Lajas, Culebra and Vieques. Heat indices in these areas may reach or exceed 112 degrees Fahrenheit (°F) during the shelf life of this product: between 10:00 a.m. and 5:00 p.m.

• The rest of the coastal towns and low elevations, as well as the municipalities around the Caguas region, will be under a heat warning between 10:00 am to 5:00 pm, at rates that can fluctuate between 108 to 111 °F.
• Heat advisory and warning should not be minimized, since there will be abundant humidity and the sensation of heat, as anticipated, in the human body could cause health complications including death, through heat stroke. Drink plenty of water, wear comfortable clothing, look for cool or shady areas, and avoid prolonged exposure to the sun. Don’t forget to take care of your pets.
• How long would we have these hot conditions? While the issuance of warnings or advisories may vary in the coming days, feelings of heat above 108°F will continue for some towns, potentially, through the middle of next week. In general, Puerto Rico will have a risk of excessive heat until the end of the upcoming work week.
• Where should it rain this Saturday? The direction of the wind should change a little from the east to a component from the southeast, which is why the rains that develop in the afternoon will mainly affect sectors in the west-northwest of the island. Additionally, it is possible that some towns in the metropolitan area will also experience some rain after midday. Towns in eastern Puerto Rico could experience passing showers in the morning hours.
• Will this day of rain be intense? No. The rain will be the product of the combination of daytime heat, the humidity of the weak tropical wave and local effects. There is presence of dust from the Sahara and there is not enough atmospheric instability to enhance a progressive development of convection (formation of heavy downpours and thunderstorms). Therefore, we would see some moderate to locally heavy showers and isolated thunderstorms, but the activity would not be significant.
• Accumulation of water may be reported on roads or in areas with poor drainage, but there should not be a problem with severe flooding. In general, the rains this Saturday would barely be able to leave between one to an inch and a half of rain. Isolated areas could accumulate up to two inches, with the activity strongest.
• Is more dust expected from the Sahara? Yes, at the moment, the haze layer present in the region is slight and has barely caused a deterioration in the air quality, whose quality index was in green this morning (good). However, a denser layer with a higher concentration of this particulate matter would arrive starting tomorrow, Sunday, and would extend until the middle of next week. During that period, air quality should deteriorate, skies would remain hazy and rain activity would be limited.
• Maritime and coastal conditions will become unstable and dangerous due to the arrival of a slight swell from the north-northwest. This event is a product of the energy caused in the northern Atlantic by Tropical Storm Idalia and atmospheric cyclones, including the dissipated Hurricane Franklin.
• The waves will be around 3 to 5 feet in Atlantic waters this morning, but will then increase to a range of 4 to 6 feet, with occasional higher swells, in the afternoon hours. The risk of marine currents is moderate for the northern beaches of the island, but will increase to high risk starting this Saturday afternoon.
• The waves in the waters of the Caribbean Sea will fluctuate between 3 to 5 feet high, although it would increase to a range of 4 to 6 feet starting tomorrow, Sunday.
• Perspective of conditions in the tropics: In addition to post-tropical cyclone Idalia, tropical storm Gert and tropical storm Katia, the National Hurricane Center monitor an area with a probability of cyclonic development. This is a tropical wave that leaves Africa this Saturday and will move towards the center of the Atlantic where it could become a tropical depression next week.

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Carlos Tolentino Rosario is a journalist who covers weather, climate change and science, among others. He holds a certification in weather forecasting from the Department of Meteorology and Atmospheric Sciences at Pennsylvania State University (PSU). He is also a member of the American Meteorological Society (AMS).