Climate and Average Weather Year Round in Isabela Puerto Rico

The climate in Isabela is warm, oppressive, windy, and partly cloudy. Over the course of the year, the temperature typically varies from 69°F to 87°F and is rarely below 66°F or above 90°F.

Based on the beach/pool score, the best time of year to visit Isabela for hot-weather activities is from late November to late April.

The temperature in Isabela varies so little throughout the year that it is not entirely meaningful to discuss hot and cold seasons.

In Isabela, the average percentage of the sky covered by clouds experiences extreme seasonal variation over the course of the year.

The clearer part of the year in Isabela begins around November 15 and lasts for 5.5 months, ending around April 30.

The clearest month of the year in Isabela is January, during which on average the sky is clear, mostly clear, or partly cloudy 81% of the time.

The cloudier part of the year begins around April 30 and lasts for 6.5 months, ending around November 15.

The cloudiest month of the year in Isabela is June, during which on average the sky is overcast or mostly cloudy 69% of the time.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Isabela varies significantly throughout the year.

The wetter season lasts 7.0 months, from April 26 to November 26, with a greater than 33% chance of a given day being a wet day. The month with the most wet days in Isabela is September, with an average of 14.1 days with at least 0.04 inches of precipitation.

The drier season lasts 5.0 months, from November 26 to April 26. The month with the fewest wet days in Isabela is March, with an average of 5.9 days with at least 0.04 inches of precipitation.

Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. The month with the most days of rain alone in Isabela is September, with an average of 14.1 days. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 49% on November 1.

Rainfall

To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. Isabela experiences significant seasonal variation in monthly rainfall.

Rain falls throughout the year in Isabela. The month with the most rain in Isabela is September, with an average rainfall of 4.3 inches.

The month with the least rain in Isabela is March, with an average rainfall of 1.1 inches.

The length of the day in Isabela varies over the course of the year. In 2024, the shortest day is December 21, with 11 hours, 1 minute of daylight; the longest day is June 20, with 13 hours, 15 minutes of daylight.

The earliest sunrise is at 5:50 AM on June 4, and the latest sunrise is 1 hour, 13 minutes later at 7:03 AM on January 18. The earliest sunset is at 5:49 PM on November 23, and the latest sunset is 1 hour, 19 minutes later at 7:08 PM on July 6.

Daylight saving time (DST) is not observed in Isabela during 2024.

The figure below presents a compact representation of key lunar data for 2024. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases.

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

Isabela experiences some seasonal variation in the perceived humidity.

The muggier period of the year lasts for 10 months, from March 24 to January 26, during which time the comfort level is muggy, oppressive, or miserable at least 84% of the time. The month with the most muggy days in Isabela is July, with 31.0 days that are muggy or worse.

The month with the fewest muggy days in Isabela is February, with 23.5 days that are muggy or worse.

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed in Isabela experiences significant seasonal variation over the course of the year.

The windier part of the year lasts for 2.6 months, from June 13 to September 1, with average wind speeds of more than 10.4 miles per hour. The windiest month of the year in Isabela is July, with an average hourly wind speed of 11.7 miles per hour.

The calmer time of year lasts for 9.4 months, from September 1 to June 13. The calmest month of the year in Isabela is October, with an average hourly wind speed of 9.1 miles per hour.

The predominant average hourly wind direction in Isabela is from the east throughout the year.

Isabela is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.

The average water temperature experiences some seasonal variation over the course of the year.

The time of year with warmer water lasts for 3.5 months, from July 27 to November 11, with an average temperature above 83°F. The month of the year in Isabela with the warmest water is September, with an average temperature of 84°F.

The time of year with cooler water lasts for 3.2 months, from January 8 to April 14, with an average temperature below 80°F. The month of the year in Isabela with the coolest water is February, with an average temperature of 79°F.

To characterize how pleasant the weather is in Isabela throughout the year, we compute two travel scores.

The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit Isabela for general outdoor tourist activities is from mid December to late March, with a peak score in the third week of January.

The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit Isabela for hot-weather activities is from late November to late April, with a peak score in the second week of January.

Methodology

For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.

Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.

Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.

Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.

Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

Temperatures in Isabela are sufficiently warm year round that it is not entirely meaningful to discuss the growing season in these terms. We nevertheless include the chart below as an illustration of the distribution of temperatures experienced throughout the year.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

The average daily incident shortwave solar energy experiences some seasonal variation over the course of the year.

The brighter period of the year lasts for 1.9 months, from March 4 to May 2, with an average daily incident shortwave energy per square meter above 6.5 kWh. The brightest month of the year in Isabela is April, with an average of 6.9 kWh.

The darker period of the year lasts for 3.9 months, from September 9 to January 7, with an average daily incident shortwave energy per square meter below 5.0 kWh. The darkest month of the year in Isabela is October, with an average of 4.6 kWh.

For the purposes of this report, the geographical coordinates of Isabela are 18.501 deg latitude, -67.024 deg longitude, and 249 ft elevation.

The topography within 2 miles of Isabela contains only modest variations in elevation, with a maximum elevation change of 423 feet and an average elevation above sea level of 170 feet. Within 10 miles contains only modest variations in elevation (1,194 feet). Within 50 miles contains very significant variations in elevation (4,442 feet).

The area within 2 miles of Isabela is covered by water (34%), cropland (23%), grassland (16%), and trees (16%), within 10 miles by water (55%) and trees (18%), and within 50 miles by water (79%) and trees (11%).