CHARLOTTE, NC (WBTV) - Seven weeks into the 2015 Atlantic Hurricane Season and so far, it's been more active than most tropical meteorologists expected.
The season got off to a quick start with Tropical Storm Ana, which developed on May 6 – three weeks before the official start of the season.
Ana came ashore near Myrtle Beach on May 10, ruining a beach weekend for many folks who endured 6-10 inches of rain on the Carolina coast. A month later, Tropical Storm Bill formed in the southern Caribbean Sea, then drifting up to Texas, making landfall on June 16.
Then just last week, Claudette formed off the mid-Atlantic coast, but stayed harmlessly out at sea.
Typically, the third "named storm" of the season does not form before mid-August. So, we're way ahead of schedule, and interestingly, two out of the three tropical storms that have formed so far this season have made landfall in the U.S. — so, again, it's not necessarily been a "quiet" season for the U.S.
So, does that mean all of those pre-season forecasts for below-average seasons were off the mark?
The three weak tropical storms that formed in near-shore warm waters may raise the overall seasonal numbers a bit, but not really change the flavor of the season.
In fact, when we look to belt where the strongest hurricanes form — the main development region just north of the Equator in the Atlantic Ocean — has been in slumber mode. Not a single storm has formed in this area thus far this season. Nothing has even been hinted at it.
And all of the primary drivers still suggest an unusually quiet Atlantic season going forward. Two of the more important factors - the strong El Nino and relatively cool deep tropical Atlantic Ocean temperatures - should limit development of the bigger, longer-lasting "Cape Verde" storms that develop from African easterly waves.
However, the very warm waters closer to the U.S. coast will continue to favor the sort of 'domestic' storms that have occurred so far this season.
Key drivers likely to lead to below-average "Big Storm" season:
- Wind shear over the Atlantic basin is higher than it has been in decades. Strong winds blowing across the development zone rip the tops off of thunderstorms, inhibiting development and organization.
- Cooler than average ocean surface temperatures. This is a main driver. Warm water fuels tropical systems. Sea temperatures of at least 82° are generally necessary and they’re nowhere to be found in the development zone. In fact, some observers have pointed out the sea surface temperatures in the region now are the coolest they’ve been in 20 years.
- High pressure and sinking air over the development zone. Rising air creates clouds and precipitation. Sinking air does just the opposite – and there’s plenty of it in place north of the Equator. Not good for storm development.
- Dust from the Sahara Desert. It’s not totally understood why, but dust coming off Africa is disruptive to both the warming of the ocean and in the formation of storms. Right now, there’s plenty of it blowing around in the tropics. Again, that’s not a good sign for storm development.
Most seasonal forecasts are lower than both the 1950-2014 average of 12/7/3 (named storms, hurricanes and major hurricanes) and the more recent "active period" (1995-2014) when the averages have been on the order of 15/8/3.
Hurricane season runs June 1 through November 30 and the peak of the season is September 10.
- Meteorologist Al Conklin