11:15 AM | *The role of weather on December 7th, 1941 and a little known important indirect benefit*

Actual hourly weather observations shown here as recorded by the weather observer at Hickam Field in Honolulu, Hawaii on the morning of December 7, 1941. The highlighted text appears to say “obstructions to visibility at this (scribbled)” and then what appears to be the word “terrified”. The obstruction to visibility at this time could have been “smoke”. The weather observer on this day was PFC Sherman Levine of the US Air Corps and he died during the attack, likely a few minutes after completing the last observation on this small slip of paper. For more on the life of PFC Sherman Levine, click here.

Overview

The weather on Oahu, Hawaii in the early morning hours of Sunday, December 7th, 1941 was not at all unusual for the time of year with mild temperatures and mainly clear skies.  Unfortunately, the weather conditions on that particular day would play a role in the bombing of the U.S. naval base by Japanese fighter planes at Pearl Harbor near Honolulu, Hawaii.  As Japanese fighters crossed the Pacific Ocean, they were given hope that their mission would succeed when the announcement was made of “clouds mostly over the mounts…visibility good”.  It is believed that the decision to attack on that particular day had plenty to do with the projected favorable weather conditions.

Pearl Harbor is in the “rain-shadow” of the Koolau Range on the south side of Oahu

Discussion

In 1941, Hawaii was a territory of the US with statehood some eighteen years away.  As early as the 1870’s, the US military had scoped out the islands for commercial and defensive potential and decided that Pearly harbor on the south side of Oahu about ten miles northwest of Honolulu fit the bill.  With the persistent trade winds blowing from the northeast most of the year, this particular part of Oahu is in the rain shadow of the Koolau Range.  While clouds and rain are common in the Koolau Range, the downsloping winds tend to dry out for southern side of the island. In fact, Honolulu averages only about 17 inches of rainfall in a given year due to the drying effects of the downsloping winds.

On the morning of December 7th, 1941, the weather observer at Hickam Field in Honolulu reported mainly clear skies each hour with mild temperatures and light east-to-northeast winds.  There was nothing that would obstruct fighter pilots lines of sight, no heavy cloud cover and no heavy rains to make flight difficult on that fateful day.  After crossing the rough waters of the North Pacific, the Japanese fighter pilots in more than 350 planes reported seeing a “long white line of coast” referring to Oahu’s Kakuku Point (according to National Geographic, AccuWeather).  In summary, as far as the weather was concerned, all was favorable for the attack that had been planned “many days or even weeks in advance” according to President Roosevelt in his famous speech given on the following day.

Though the US suffered greatly on that particular morning due in large part to the generally clear sky conditions, the weather actually played an important indirect beneficial role for the nation.  The USS Enterprise (CV-6) was coming back to Pearl Harbor from Wake Island and was actually scheduled to arrive on the morning of December 7th, but it was delayed due to rough seas.  According to the former director for the US Naval Institute, Paul Stillwell, “the vessel was behind schedule returning to Pearl Harbor, and because of this was not present for the attack. The Enterprise played a substantial role throughout the remainder of the war, and had it been in port that day, things may have been very different.” 

Aerial view of USS Enterprise at sea in 1945 (courtesy Wikipedia)

USS Enterprise (CV-6) was the seventh U.S. Navy vessel to bear the name. Colloquially called "The Big E", she was the sixth aircraft carrier of the United States Navy. A Yorktown-class carrier, she was launched in 1936 and was one of only three American carriers commissioned before World War II to survive the war. Had the mighty vessel made it back to Pearl Harbor on schedule, she would have been engaged by Japanese fighters and likely damaged or destroyed. As it turned out, the USS Enterprise earned enough commendations (20 Battle Stars) to become the most decorated US ship in World War II.

Pennsylvania Military Museum in Boalsburg, PA has two of the guns from the USS Pennsylvania

One of the battleships damaged at Pearl Harbor was the USS Pennsylvania (BB-38).  After a three month repair, it returned to action in 1942. On August 12th, 1945, three days before Japan surrendered, the USS Pennsylvania was extensively damaged by a Japanese torpedo at Okinawa.  The torpedo's impact caused a hole of approximately 30 feet in diameter in her stern. Twenty men were killed and ten were injured. Two of the ships 14 inch guns are now on display at the Pennsylvania Military Museum in Boalsburg, PA (source Dr. Jon Nese, Penn State University: video discussion).

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com