Hawaii is typically a place people think of with a wistful sigh: tropical beaches, lush greenery, and weather so reliable the forecast hardly budges. The fiftieth state has had a hard time living up to that third point, and the state’s long-lasting drought could return and get worse if El Niño lives up to its bluster.
Just over 65% of Hawaii is abnormally dry or worse as of last Tuesday’s analysis, with the worst drought conditions affecting Maui and Kauai. The major population centers are largely unaffected right now, but the dry land will start affecting crops in the next month or two if beneficial rain doesn’t help put the state back on the right track.
Even though the state is firmly in the tropics, drought is nothing new in Hawaii. In fact, this drought is nothing compared to the arid streak they went through a couple of years ago—just this year did Hawaii start to return to normal from a lengthy drought that lasted from 2008 through the beginning of 2014.
The island chain’s wet season usually begins around the beginning of November and lasts through April; the average yearly precipitation (Oct. 1 to Sept. 30) in Honolulu is about 17 inches, which is right around what Salt Lake City sees during the same time period, to give you a reference point. Honolulu Airport has seen 11.50 inches of rain between October 1, 2014, and today, which is about four inches below normal. As so many people from Texas or California or Florida can tell you, those seemingly-small deficits can add up in a hurry.
The Little Boy
El Niño seems like yet another trendy scapegoat for all of our bad weather of late (replacing the evil polar vortex for now), but the sudden warming of the equatorial waters in the eastern Pacific really can have a wide-reaching effect on global weather patterns. One of its biggest effects known to us here in the United States is the tendency for the subtropical jet stream to jut northward, giving the southern half of the country (from California to the southeast) the potential to see a wetter-than-normal winter.
Hawaii, on the other hand, is negatively affected by this shift in weather patterns. Stronger El Niño events are strongly linked to devastating droughts and wildfires in this part of the world, especially in Oceania. Hawaii, like many other islands in the Pacific, tends to stay dry when an El Niño is present, and that’s not a good thing when you’re just coming off the tail-end of a drought that lasted for nearly six years.
All indications point toward a robust El Niño this year, with waters warming up to levels we haven’t seen since the Super Scary Adjective El Niño of 1997-1998. Sea surface temperatures in the equatorial Pacific are well above normal, and stronger El Niño events lead to greater odds of weather patterns affected by the oceanic warming.
Heavy Rain (Or Lack Thereof)
The location and geography of each island in Hawaii makes it hard to analyze the state’s precipitation as a whole. A great example of this is Maui—up in Kahului, they’ve had so much rain this year that they’re sitting nine inches above average, but just a few miles away, the southern part of the island is dipping into “severe drought” territory. Here, I’ll focus on precipitation in Honolulu.
Above is a chart showing observed precipitation (green line/shading) versus normal precipitation (brown line) in Honolulu between October 1, 1997 and September 30, 1998, a period during which that historic El Niño occurred. Precipitation was hard to come by in the Aloha State, with rainfall coming in at just 36% of average for the water year. The same trend holds true for the El Niños of 2002-2003, 2006-2007, and 2009-2010.
Here’s what the 2014-2015 water year looks like so far:
At first glance, it looks like we’re sitting pretty, but a huge chunk of that rain came in one wallop, which isn’t very helpful in the long-term. Extensive heavy rainfall last October—a result of Tropical Storm Ana and its remnants—pushed Honolulu into a good spot for the year, but if you were to remove that anomalous day, rainfall would be far below average this water year.
Everything points toward the idea that Hawaii is going to slip back into the drought from which it just started to recover. If history is a good guide, it looks like rain will be harder to come by over the coming months as El Niño takes hold and strengthens to levels we haven’t seen in nearly 20 years. While the lack of rain is great for beachgoing tourists, a dry streak that lasts for too long could negatively effect the state’s lucrative agricultural industry—including pineapples, coffee, and macadamia nuts—not to mention the harm done to water supplies and folks who rely on rainwater for personal use.