U.S. tornadoes that occur outside the U.S. … the continental U.S. that is!

We’re all familiar with the idea of Tornado Alley and the tornadoes that occur across the continental United States.  Regions from the Great Plains all the way east across the Appalachians and beyond experience tornadoes annually; even areas along the West Coast including California and even Oregon and Washington regularly experience tornadoes.   What about areas of the United States outside of the lower-48?  Such as Alaska, Hawaii, and Puerto Rico?

Related: Monthly tornado averages by state and region

Using a combination of the Storm Prediction Center tornado database and the National Climatic Data Center (NCDC) storm events page it was possible to investigate the number of tornado events that have occurred in these areas from 1950-2012.

Alaska

Out of all 50 states, Alaska is the state that has the lowest number of recorded tornadoes.  There have only been four recorded tornado events since 1950, the last of which occurred on August 25^th, 2005.  All tornadoes have been rated at the F/EF0 level.  Referring to the map, the majority of the tornadoes have occurred in the southwestern part of the state, where the terrain is flatter and the climate is moderated and more maritime in nature due to proximity to the Gulf of Alaska.

Alaska is the largest state in the United States, with a land area of 570,380 square miles.  Considering it only has four confirmed tornadoes since 1950, this equates to a ratio of one tornado for every 142,595 square miles.  In comparison, Oklahoma currently boasts a ratio of one tornado for every 20 square miles!

Basically, Alaska is not a tornado state — it currently experiences one tornado roughly once every 15 years.

Puerto Rico

Puerto Rico is a marginal region for tornado activity.  Characterized by steep and rugged terrain over the western and northwestern portion of the territory, most tornadoes occur on the west coast over flatter land where the easterly trade winds collide with the sea breeze.

There have been 23 tornado events since 1950, with the most recent one occurring fairly recently on September 13^th, 2012.  Similar to Alaska, the recorded tornadoes over Puerto Rico have all been week, with only one attaining higher than F0/EF0 status.

Hawaii

When it comes to discussing U.S. regions outside of the continental United States, Hawaii is the “tornado alley” of them all.

There have been about 40 tornadoes since 1950, with the last tornado occurring on March 9^th, 2012.  Like Alaska and Puerto Rico, the tornadoes have predominantly been F0/EF-0 in rank, but a handful of F2s have also struck several of the islands.  Referring to the map, most tornadoes occur on the island of Oahu (where Honolulu is located); one reason could be that Oahu holds the highest population of all the islands, and it is also the island with a National Weather Service WFO.

It is important to note the 41 tornado reports do not include waterspouts which don’t come ashore!  The National Climatic Data Center shows a record of 31 waterspout reports from 1996-2012 across the entire island chain, and again with most waterspout reports are from Honolulu.

Conclusion

Tornadoes do in fact occur in the states and territories of the United States outside of the continental and lower 48, but the number pales in comparison.  A single state in tornado alley can experience more tornadoes in one year (or even a day!) than Alaska, Hawaii, and Puerto Rico combined.

While it is important to note that one possible reason why the total tornado numbers are low is likely due to the sparse population in parts of these areas, it’s also likely that regardless of a low reporting rate these areas actually experience low tornado rates.

Additional research of tornado climatology for other United States territories outside of the lower 48 likewise yielded paltry results: neither American Samoa, nor Virgin Islands, nor Guam have any tornado reports to date.  (Although the British Virgin Islands has one tornado report!)

Bottom line: for those interested in studying the science behind tornadoes and witnessing this particular wonder of nature, stick to the continental United States!