Climate and Average Weather Year Round in Northern Mariana Islands Northern Mariana Islands

In Northern Mariana Islands, the wet season is overcast; the dry season is partly cloudy; and it is hot, oppressive, and windy year round. Over the course of the year, the temperature typically varies from 76°F to 88°F and is rarely below 73°F or above 90°F.

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

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

In Northern Mariana Islands, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.

The clearer part of the year in Northern Mariana Islands begins around November 5 and lasts for 6.1 months, ending around May 10.

The clearest month of the year in Northern Mariana Islands is March, during which on average the sky is clear, mostly clear, or partly cloudy 52% of the time.

The cloudier part of the year begins around May 10 and lasts for 5.9 months, ending around November 5.

The cloudiest month of the year in Northern Mariana Islands is August, during which on average the sky is overcast or mostly cloudy 91% 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 Northern Mariana Islands varies very significantly throughout the year.

The wetter season lasts 3.9 months, from July 7 to November 3, with a greater than 32% chance of a given day being a wet day. The month with the most wet days in Northern Mariana Islands is September, with an average of 18.1 days with at least 0.04 inches of precipitation.

The drier season lasts 8.1 months, from November 3 to July 7. The month with the fewest wet days in Northern Mariana Islands is March, with an average of 1.3 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 Northern Mariana Islands is September, with an average of 18.1 days. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 62% on September 23.

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. Northern Mariana Islands experiences extreme seasonal variation in monthly rainfall.

Rain falls throughout the year in Northern Mariana Islands. The month with the most rain in Northern Mariana Islands is August, with an average rainfall of 8.9 inches.

The month with the least rain in Northern Mariana Islands is March, with an average rainfall of 0.5 inches.

The length of the day in Northern Mariana Islands varies over the course of the year. In 2025, the shortest day is December 22, with 11 hours, 14 minutes of daylight; the longest day is June 21, with 13 hours, 2 minutes of daylight.

The earliest sunrise is at 5:45 AM on June 3, and the latest sunrise is 1 hour, 1 minute later at 6:47 AM on January 21. The earliest sunset is at 5:43 PM on November 22, and the latest sunset is 1 hour, 8 minutes later at 6:51 PM on July 8.

Daylight saving time (DST) is not observed in Northern Mariana Islands during 2025.

The figure below presents a compact representation of key lunar data for 2025. 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.

The perceived humidity level in Northern Mariana Islands, as measured by the percentage of time in which the humidity comfort level is muggy, oppressive, or miserable, does not vary significantly over the course of the year, staying within 2% of 98% throughout.

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 Northern Mariana Islands experiences significant seasonal variation over the course of the year.

The windier part of the year lasts for 6.3 months, from October 23 to May 1, with average wind speeds of more than 14.3 miles per hour. The windiest month of the year in Northern Mariana Islands is December, with an average hourly wind speed of 17.3 miles per hour.

The calmer time of year lasts for 5.7 months, from May 1 to October 23. The calmest month of the year in Northern Mariana Islands is August, with an average hourly wind speed of 11.7 miles per hour.

The predominant average hourly wind direction in Northern Mariana Islands is from the east throughout the year.

Northern Mariana Islands 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 does not vary significantly over the course of the year, remaining within 2°F of 83°F throughout.

To characterize how pleasant the weather is in Northern Mariana Islands 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 Northern Mariana Islands for general outdoor tourist activities is from early January to early April, with a peak score in the last week of February.

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 Northern Mariana Islands for hot-weather activities is from late November to late April, with a peak score in the last week of March.

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 Northern Mariana Islands 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 significant seasonal variation over the course of the year.

The brighter period of the year lasts for 2.5 months, from March 5 to May 19, with an average daily incident shortwave energy per square meter above 6.4 kWh. The brightest month of the year in Northern Mariana Islands is April, with an average of 7.0 kWh.

The darker period of the year lasts for 3.7 months, from July 10 to November 2, with an average daily incident shortwave energy per square meter below 4.6 kWh. The darkest month of the year in Northern Mariana Islands is September, with an average of 4.1 kWh.

For the purposes of this report, the geographical coordinates of Northern Mariana Islands are 15.214 deg latitude, 145.756 deg longitude, and 223 ft elevation.

The topography within 2 miles of Northern Mariana Islands contains very significant variations in elevation, with a maximum elevation change of 1,427 feet and an average elevation above sea level of 392 feet. Within 10 miles also contains very significant variations in elevation (1,532 feet). Within 50 miles also contains very significant variations in elevation (1,532 feet).

The area within 2 miles of Northern Mariana Islands is covered by cropland (79%) and trees (14%), within 10 miles by water (89%), and within 50 miles by water (99%).