PEARL Harbor Day 2021 marks the 80th anniversary of Japan’s sneak attack on the US Navy Base in Hawaii.

The honor, courage and sacrifice of the 2,403 lives lost and 1,178 injured is acknowledged around America today.

Looking back at the attack, weather played a huge role that day and it played a huge role in the days after.

After the Pearl Harbor attack, the U.S. Weather Bureau – – the predecessor to the modern-day National Weather Service – – announced it would immediately cease publication of nearly all weather observations and forecast data, lest it fall into the hands of our enemy.

In order to understand why, we must first talk about the day of the attack.

Weather was very important in the decision made by the U.S. military to place a naval base at Pearl Harbor.

The harbor was located in the rain shadow of the Koolau Range due to the persistent northeast trade winds. This would often place most of the low clouds and precipitation on the northeast side of the mountain range. So as the air descended the range, it dried and cleared out the clouds and precipitation. This made it a prime location to have an operational Naval base on the southeast side of Oahu. A naval base located on the island chain of Hawaii would give the United States a strategic military advantage in the Central Pacific.

Well, the Japanese were also aware of this advantage. They planned to eliminate any threat to them from the United States by attacking it’s fleet of ships anchored at Pearl Harbor.

The Japanese fleet left northern Japan on November 26th, 1941, and traveled across the Northern Pacific. It was a treacherous journey, and this journey was made under near-complete radio silence. Then on December 7th, 1941, they arrived north of Hawaii and launched more than 350 aircraft from the fleet of six aircraft carriers and around 50 other ships toward the unsuspecting base at Pearl Harbor.

At first, these aircraft encountered clouds but then the clouds began to clear out thanks to the previous mentioned downsloping winds.

With good visibility and only scattered clouds, the Japanese had a relatively clear window for the attack.

The attack lasted 75 minutes.

President Franklin Roosevelt delivered his famous speech on December 8, 1941, about the horrifying attack on Pearl Harbor the previous day. In his speech, he stated “that the attack was deliberately planned many days or even weeks” in advance.

Japanese spy Takeo Yoshikawa fed information about the naval base’s ship movements, as well as weather conditions, back to enemy forces (according to the U.S. Naval Institute). After deciding the highest number of ships would be in port on the morning of December 7th, Yoshikawa notified his commanding officers to move forward.

The following message went out to daily weather recipients… “Owing to the value of weather reports and forecasts to the enemy, the Weather Bureau, at the request of military authorities, has curtailed the publication of current weather data. However, special warnings of severe or dangerous weather conditions, such as storms and cold waves, will be given as wide dissemination as practicable, including radio broadcast. The Weather Bureau will resume regular service in whole or in part when such resumption may be accomplished without detriment to the national defense.

In accordance with the above policy, the daily distribution of the Washington Weather Map has been discontinued. One week after date of issue a limited number of copies will be distributed for record, instruction and other purposes to a list of those who make written application to the Chief of the U.S. Weather Bureau. The applications should state in detail the proposed use of the map. Appropriate refunds will be made for unexpired subscriptions.”

There were thoughts that there were spies in place that would share data with the enemy. The thought was the enemy would look for weather windows of opportunity to mount attacks.

While this movement may seem extreme by today’s standards, it’s a practice that still occasionally happens. When I was an intern with the international weather department of CNN, we would often see missing weather data from Middle Eastern countries. This was back in 2001 when I was learning from retired Navy meteorologists. They taught me this was a possible sign that something was about to happen… a possible strike of some sort.

Weather even played a critical role in the timing and potential success of the dramatic raid that lead to the death of Osama bin Laden.

The mission to capture or kill bin Laden was scrubbed on Saturday night/early Sunday due to bad weather in Pakistan. A front blew through the area with high winds and there were thunderstorms in the area, forcing the military to scrub the mission Saturday night.

Then on Sunday night, they got the green light. The sky was clear and moonless. The weather was ideal for the pilots to drop in from above and go undetected. Also, the air was calm. Visibility was lower at 2.5 with haze reported. This may have been a critically beneficial factor in favor of U.S. Special Forces that night.

It’s only recently that governments agreed in 2021 to exchange climate and weather data freely in a landmark decision at the World Meteorological Congress, which had a meeting in October in Geneva.

After four years of negotiations, the 193 member countries of the World Meteorological Organization (WMO) adopted a resolution making it mandatory for them to collect certain information in their territories and share it with fellow members. 

The WMO, which coordinates the data exchange between its members, hadn’t updated its policy since its adoption in 1995 and was in urgent need of getting up to speed with scientific and technological developments as well as the worsening impacts of climate change.

Why it’s important.  

Humidity, temperature as well as wind speed and direction are among the most basic measures needed to forecast the weather, making it key to prepare for disasters such as droughts, floods and hurricanes. 

As such extreme weather events worsen due to global warming, countries have become more open to cooperating to tackle climate challenges.

“The atmosphere doesn’t have any borders,” Lars Peter Riishojgaard, director of the WMO’s Earth system branch, told Geneva Solutions.

“Weather and climate are global phenomena, and what this means for computer models is that you need to start with a model that includes the entire global atmosphere,” he said.

Models use information from as far back as the 1850s to understand and predict climate change patterns, however there are huge voids in certain regions such as Africa and the Pacific Ocean, where data is collected and exchanged sporadically.

“Many developing countries don’t have either the technical or the financial resources to actually [collect data] to the fullest extent. And some countries have the technical and financial resources, but have been reluctant to share the information that they have,” Riishojgaard explained.

The regulation adopted will require countries to locally collect certain key measurements that satellites cannot provide, including temperature, humidity, wind speed and direction at least up to 20 km in altitude as well as surface pressure, which will have to be taken every 200km every hour.