Climate and Average Weather Year Round in Rongelap Marshall Islands

In Rongelap, the wet season is windy and overcast, the dry season is extremely windy and mostly cloudy, and it is warm and oppressive year round. Over the course of the year, the temperature typically varies from 80°F to 83°F and is rarely below 78°F or above 84°F.

Based on the beach/pool score, the best times of year to visit Rongelap for hot-weather activities are from mid May to late June and from early December to late April.

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

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

The clearer part of the year in Rongelap begins around November 23 and lasts for 5.1 months, ending around April 25.

The clearest month of the year in Rongelap is February, during which on average the sky is clear, mostly clear, or partly cloudy 33% of the time.

The cloudier part of the year begins around April 25 and lasts for 6.9 months, ending around November 23.

The cloudiest month of the year in Rongelap is September, during which on average the sky is overcast or mostly cloudy 82% 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 Rongelap varies significantly throughout the year.

The wetter season lasts 5.0 months, from June 24 to November 24, with a greater than 28% chance of a given day being a wet day. The month with the most wet days in Rongelap is September, with an average of 14.5 days with at least 0.04 inches of precipitation.

The drier season lasts 7.0 months, from November 24 to June 24. The month with the fewest wet days in Rongelap is February, with an average of 1.5 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 Rongelap is September, with an average of 14.5 days. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 52% on September 28.

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. Rongelap experiences extreme seasonal variation in monthly rainfall.

The rainy period of the year lasts for 11 months, from February 28 to January 16, with a sliding 31-day rainfall of at least 0.5 inches. The month with the most rain in Rongelap is September, with an average rainfall of 4.6 inches.

The rainless period of the year lasts for 1.4 months, from January 16 to February 28. The month with the least rain in Rongelap is February, with an average rainfall of 0.3 inches.

The length of the day in Rongelap does not vary substantially over the course of the year, staying within 46 minutes of 12 hours throughout. In 2024, the shortest day is December 21, with 11 hours, 28 minutes of daylight; the longest day is June 21, with 12 hours, 47 minutes of daylight.

The earliest sunrise is at 6:28 AM on May 31, and the latest sunrise is 48 minutes later at 7:16 AM on January 27. The earliest sunset is at 6:25 PM on November 18, and the latest sunset is 55 minutes later at 7:20 PM on July 10.

Daylight saving time (DST) is not observed in Rongelap 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.

The perceived humidity level in Rongelap, 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, remaining a virtually constant 100% 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 Rongelap experiences extreme seasonal variation over the course of the year.

The windier part of the year lasts for 7.7 months, from November 7 to June 29, with average wind speeds of more than 14.9 miles per hour. The windiest month of the year in Rongelap is December, with an average hourly wind speed of 18.7 miles per hour.

The calmer time of year lasts for 4.3 months, from June 29 to November 7. The calmest month of the year in Rongelap is September, with an average hourly wind speed of 11.2 miles per hour.

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

Rongelap 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 82°F throughout.

To characterize how pleasant the weather is in Rongelap 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 Rongelap for general outdoor tourist activities is from early January to mid March, with a peak score in the third 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 times of year to visit Rongelap for hot-weather activities are from mid May to late June and from early December to late April, with a peak score in the third week of February.

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 Rongelap 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 2.7 months, from February 14 to May 5, with an average daily incident shortwave energy per square meter above 6.4 kWh. The brightest month of the year in Rongelap is March, with an average of 6.8 kWh.

The darker period of the year lasts for 3.3 months, from August 8 to November 16, with an average daily incident shortwave energy per square meter below 4.8 kWh. The darkest month of the year in Rongelap is October, with an average of 4.4 kWh.

For the purposes of this report, the geographical coordinates of Rongelap are 11.164 deg latitude, 166.894 deg longitude, and 36 ft elevation.

The topography within 2 miles of Rongelap is essentially flat, with a maximum elevation change of 46 feet and an average elevation above sea level of 1 foot. Within 10 miles is also essentially flat (46 feet). Within 50 miles is also essentially flat (82 feet).

The area within 2 miles of Rongelap is covered by water (100%), within 10 miles by water (100%), and within 50 miles by water (100%).