National Weather Service United States Department of Commerce

Coastal Storm Impacting the Mid-Atlantic and Northeast; Weekend Rain May Hasten Midwest Flooding

A strengthening storm moving north along the East Coast will continue heavy rain across the Mid-Atlantic into southern New England into Friday while points further north and west will see some locally heavy snow and strong, potentially damaging, winds. In the Midwest, rainfall may worsen ongoing flooding this weekend. In the West, a Pacific front will bring rain and mountain snow Friday. Read More >

Weather Outlook


Heat Threat





Heat Index, Temperature, Relative Humidity and Surface Wind Forecast

San Juan





Heat Index Criteria


Heat Advisory means that Heat Index values of 108°F* or greater are expected generally within the next 24 hours. Consider postponing or rescheduling any strenuous outdoor activities. If you must be outside, be sure to drink plenty of water and take frequent breaks in the shade. 

An Excessive Heat Watch means that Heat Index values are expected to reach or exceed 113°F* beginning in the next 12 to 48 hours. Stay informed and plan ahead.  

An Excessive Heat Warning means that Heat Index values are expected to reach or exceed 113°F* within the next 24 hours. Refrain from outdoor activities of any nature during the warmest time of the day. Drink plenty of water and take frequent breaks if you must be outside. Stay indoors in an air conditioned building as much as possible.


*The criteria listed above was a collaboration between WFO San Juan and  Department of Environmental Health, University of Puerto Rico - Medical Sciences Campus. 

Méndez-Lázaro P, Muller-Karger FE, Otis D, McCarthy MJ, Rodríguez E. A heat vulnerability index to improve urban public health management in San Juan, Puerto Rico. Int J Biometeorol. 2017 Feb 17. doi: 10.1007/s00484-017-1319-z
Méndez-Lázaro PA, Pérez-Cardona CM, Rodríguez E, Martínez O, Taboas M, Bocanegra A, Méndez-Tejeda R. Climate change, heat, and mortality in the tropical urban area of San Juan, Puerto Rico. Int J Biometeorol. 2016 Dec 15. doi10.1007/s00484-016-1291-z

Méndez-Lázaro P, Martínez-Sánchez O, Méndez-Tejeda R, Rodríguez E, Morales E, et al. (2015) Extreme Heat Events in San Juan Puerto Rico: Trends and Variability of Unusual Hot Weather and its Possible Effects on Ecology and Society. J Climatol Weather Forecasting 3: 135. doi:10.4172/2332-2594.1000135


Heat Safety 


Stay cool, stay hydrated, and stay informed!



Heat is the #1 weather-related killer in the United States! Here are a few tips on staying safe during episodes of dangerously hot weather:

  • Children and pets should never be left unattended in vehicles under any circumstances. This is especially true during warm or hot weather when car interiors can reach lethal temperatures in a matter of minutes.
  • Take extra precautions if you work or spend time outside. When outdoors, wear sunblock and light colored clothing as well as a wide-brimmed hat to keep your head and body cooler. Limit strenuous outdoor activities and take frequent rest breaks in shaded or air conditioned environments. When possible, reschedule strenuous activities to early morning or evening.
  • Drink more water than usual and avoid alcohol, sugar, and caffeine.
  • Recognize the signs and symptoms of heat illness. Early symptoms include headache, thirst, and muscle cramps. Serious symptoms include weakness, skin that is cool to the touch, fast but weak pulse, nausea, and fainting. Severe symptoms include hot and red dry skin, fast and strong pulse, sweating that has stopped, and unconsciousness. Untreated heat illness can lead to a fatal heat stroke.

For more information, check the National Weather Service's Heat Safety page.