Pearl Harbor attack led to the halt of weather data publication

Dec 7, 2023, 10:13 AM

Image: The pass-in-review by the USS William P. Lawrence (DDG 110) can be seen as Pearl Harbor comm...

The pass-in-review by the USS William P. Lawrence (DDG 110) can be seen as Pearl Harbor commemorates the 78th Anniversary of World War II attacks at the Pearl Harbor National Memorial in Honolulu on Dec. 7, 2019. (Photo: Kat Wade, Getty Images)

(Photo: Kat Wade, Getty Images)

As President Franklin D. Roosevelt stated the day after the attack on the Pearl Harbor, the U.S. Naval base outside of Honolulu, “December 7, 1941 – a date which will live in infamy.”

Days later, the precursor to today’s National Weather Service, the U.S. Weather Bureau, announced it would cease publication of nearly all weather observations and forecast data to avoid having it fall into enemy hands. This announcement was in coordination with U.S. military forces, particularly the U.S. Army.

First, the publication of weather data along the West Coast west of the Cascades and the Sierra Mountains was curtailed. Offshore weather observations and forecasts followed on Dec. 13. About a week after the attack, public weather information restrictions expanded across the nation.

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In that era, weather information was shared with the public via radio and newspapers, as well as postings in post offices, rail stations, and other public places. The U.S. Coast Guard broadcast marine weather information on their radio channels.

Weather information at that time was rather primitive compared to the resources of the 21st century. The data at the time included a daily weather map with the latest high and low temperatures, rainfall amounts, current weather and barometer conditions.

The only exception to these weather data restrictions was the radio broadcast of any severe weather bulletins, and even those would not reference cloud formations, barometric pressure and wind conditions. Coastal marine forecasts would only use pennants or flags at the shore to denote small craft advisories, gale, storm or hurricane warnings.

Image: A U.S. weather map from 1941 (Image courtesy of the National Oceanic and Atmospheric Administration Virtual Lab)

A U.S. weather map from 1941 (Image courtesy of the National Oceanic and Atmospheric Administration Virtual Lab)

There was the suspicion that spies were already in place and would share that weather data with the enemy, who then would look for weather windows of opportunity to mount attacks.

According to an article published in the New York Times on Dec. 16, 1941, nine days after the attack, “Daily bulletins containing limited temperature and precipitation data will be issued on specific authority of the chief of the Weather Bureau, F.W. Reichelderfer. They will contain no information of wind directions, positions of storm centers, air-mass fronts or ‘other facts of actual or potential value to enemy interests.'”

Reichelderfer went on to tell The New York Times, “All our facilities are now geared to serve the war program to the fullest possible extent, and we are doubling that advantage to our own forces by withholding it completely from our enemy.”

The U.S. Weather Bureau continued to collect data and produce hand-plotted current and forecast information, but it was only shared with military and other public safety authorities, and archived for future historical use. Those public safety authorities who needed data for critical operations included utilities, transportation organizations, and heating companies, shared with safeguards to keep the information in-house and not become public.

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The weather information restrictions for the public remained in place for close to two years. Most of the restrictions were lifted on Oct. 31, 1943, with the exception of barometric pressure and wind direction reports. By then and with winter approaching, officials felt the potential value to the enemy was quite low and justified easing the weather information restrictions to help support aircraft operations, boating and shipping, agriculture and more.

Ted Buehner is the KIRO Newsradio meteorologist. You can read more of Ted’s stories here and follow him on X, formerly known as Twitter.

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