Call it a meteorological mystery: Forecasters warned that there would be at least six Atlantic hurricanes this season, but so far we've seen only one.
It's the first year in recent memory that every major hurricane forecast has busted after pointing to "above normal activity."
We are passing the season's halfway point. Normally, the Atlantic would see its first hurricane by August 10, and a major hurricane (Category 3 or higher) by September 4.
But this year is not normal.
2013's first hurricane -- Humberto -- was a month late. It was so behind schedule it nearly set a record for tardiness.
Although the number of 2013 Atlantic storms is above average -- at nine so far -- the intensity of those storms hasn't matched the forecasts. Humberto -- a Category 1 with winds under 95 mph -- ranked nowhere close to a major hurricane when it spun out harmlessly in the mid-Atlantic.
What's going on here? Climate change? El Niño? Something else?
Experts don't have a full understanding, but three things are getting the blame:
-- In the eastern Atlantic, where hurricanes are often born, African desert air is drying the moisture that hurricanes need to form.
-- In the western Atlantic and Gulf of Mexico, fast horizontal winds have been cutting off the tops of potential hurricanes, sapping their power.
-- Experts speculate that dry air from Brazil's drought may be another factor.
Respected veteran hurricane scientist Bill Gray of Colorado State University has pretty much given up for this year.
His research group predicted eight hurricanes this season. "The forecast up to now is a bust," says Gray. "The second half of the season will be more active," he predicts, with as many as five more hurricanes. Even with the most sophisticated prediction techniques, Gray says, "there's still 40 percent or 50 percent of variations in tropical storm and hurricane activity that we can't explain."
Poking fun at his government rivals, Gray jokes about "reports of a suicide watch" among the meteorologists who worked on this year's National Weather Service forecast. Nonetheless, the feds are standing firm.
Unlike Gray, they're not ready to cry uncle.
"Our forecast remains the same," weather service spokesman Chris Vaccaro said. "We're sticking by it."
The NWS -- last May -- initially forecast 13 to 20 "named storms," including seven to 11 hurricanes. Then in August, it dialed down that initial forecast to predict 13 to 19 named storms, including six to nine hurricanes.
So far, including Humberto, we've seen nine named storms. From the weather service's perspective, that statistic shows its forecast remains valid.
"In some ways we're ahead of schedule," says Vaccaro. "And in late September and October there's plenty of time for the number of tropical storms and hurricanes to climb." According to the weather service forecast, at least four more tropical storms or hurricanes will form in the next 11 weeks. That's 77 days, or one storm forming every 19 days.
It would be a mistake to believe that the second half of any hurricane season would resemble the first half, says Vaccaro, who stresses that we're not experiencing a "lull." "Historically speaking, June and July and the first part of August are typically fairly quiet," he says. September, he warns, is the time when storms can start to get get serious.
Some key examples:
-- Hurricane Gloria hit the eastern United States in September 1985.
-- In 1938, a disastrous hurricane tore up parts of the northeast, also during the month of September.
-- In 1998 one of the deadliest storms on record, Hurricane Mitch, raked the Caribbean and Central America after forming in late October.
-- Hurricane Sandy, which altered so many lives last year when it slammed into much of the Eastern Seaboard, didn't appear until October.