Historic Tropical Cyclone Drought
EL NIÑO and La Niña are commonly associated with devastating floods and crippling droughts, but the current transition from El Niño to La Niña is aiding one drought that can certainly be viewed as a positive: There hasn't been a named tropical system in the Northwest Pacific since December 17, 2015. As of Friday, that makes 198 days without a storm, tying the previous longest stretch.
The Northwest Pacific is the most active basin in all of the tropics, averaging 27 named storms per year. Unlike each of the other basins around the globe, the Northwest Pacific doesn't have a defined season -- the season is simply the entire calendar year.
In 2015 there was a lot of publicity about El Niño warming the Pacific and enhancing tropical cyclone activity. It seemed as if every named storm was blowing up into a monster. During 2015, there were a record 26 category 4 or 5 storms in the northern hemisphere, with the large majority of those occurring in the Pacific.
This raced past the previous record of 18 category 4-5 storms.
Now that El Niño is officially dead, we are rapidly heading toward the La Niña phase. According to the Climate Prediction Center, there is a 75% chance of La Niña developing by the fall. This comes as no surprise as the historical record shows that all of the strongest El Niño's have been immediately followed by a La Nina event.
So what is the difference between the two?
La Niña is the cool phase of the El Ninosouthern Oscillation (ENSO) climate pattern - a naturally occurring phenomenon that involves fluctuating ocean temperatures in the Pacific.
La Niña is the opposite of El Niño, which is the warm phase of the cycle.
El Niño is characterized by a warming of the waters in the central and eastern Pacific Ocean. La Niña features a cooling of those same Pacific waters.
History shows that we can expect a tropical cyclone drought in the Northwest Pacific during years that transition from a strong El Niño to a La Niña. While El Niño created warm waters and enhanced activity in 2015, the strong El Niño can also be blamed for the lack of activity during the first half of 2016.
According to Dr. Phil Klotzbach, a research scientist at Colorado State University, "El Niño's force mass subsidence during the early part of the Northwest Pacific tropical cyclone season." This essentially puts a lid on the atmosphere, preventing thunderstorm activity from organizing into tropical storms and typhoons.
According to Klotzbach, the four longest droughts in West Pacific history have occurred in 1973, 1983, 1998 and 2016. In each of these years, we were in the waning period of a strong El Niño.
Klotzbach notes that in each of the previous occurrences the entire season continued to have well below average activity. While a typical season averages 27 named storms and 17 typhoons (the equivalent of a hurricane in the Atlantic and East Pacific), 1973, 1983, and 1998 averaged just 21 named storms and 11 typhoons.
The transition to La Niña is also helping to set records in the East Pacific. The season officially started on May 15, but as of the end of June we still haven't had a single named storm -- a record for the latest start, according to Klotzbach.