Atlantic Goes Into a Slumber; Here's What NOAA Expects the Rest of the Hurricane Season

Chris Dolce
Published: August 11,2016
NOAA released its updated forecast for 2016 Atlantic hurricane season on Thursday, saying it expects the most active season since 2012. This is not surprising, however, since the last three Atlantic hurricane seasons have been rather tame.
The Atlantic is in a bit of a mid-August slumber at the moment, but we are in a stretch of months now that are historically the most active.
(MORE: When Atlantic Hurricane Season Ramps Up)

Updated NOAA Hurricane Season Forecast

The forecast from NOAA says that the chance of a near-average or above-average Atlantic hurricane season has increased over its initial projections in May.
NOAA's forecast calls for a 70 percent chance of 12-17 named storms, 5-8 hurricanes, and 2-4 major hurricanes (Category 3 or stronger on the Saffir-Simpson Hurricane Wind Scale). This includes the five named storms that have already formed in the Atlantic during the 2016 season, two of which have become hurricanes (Alex and Earl).

Numbers of Atlantic Basin named storms, those that attain at least tropical storm strength, hurricanes, and hurricanes of Category 3 intensity forecast by NOAA, Colorado State University and The Weather Company compared to the 30-year average.

The NOAA hurricane season forecast is similar to the numbers in an update from Colorado State University (CSU) last week along with the late-July forecast from The Weather Company, an IBM business.
(MORE: CSU Forecast Update)
“We’ve raised the numbers because some conditions now in place are indicative of a more active hurricane season, such as El Niño ending, weaker vertical wind shear and weaker trade winds over the central tropical Atlantic, and a stronger west African monsoon,” said Dr. Gerry Bell, lead seasonal hurricane forecaster at NOAA’s Climate Prediction Center.
Having weaker vertical wind shear, or weaker winds aloft, is important for the development of tropical storms and hurricanes. This is because shower and thunderstorm activity can remain collocated with surface low pressure instead of getting blasted away by strong winds.
Last year, El Niño kept strong winds aloft in place in over parts of the Atlantic basin, which in combination with dry air, led to the demise of several Atlantic storms.
Bell mentioned that the season should not be "extremely active" due to several other environmental factors.
NOAA also announced Thursday that La Niña is only "slightly favored to develop during the hurricane season". Bell said that if it did develop, it would be weak and have no significant impact on the hurricane season.

Why is the Atlantic in a Mid-August Slumber?

After the landfalls of Earl in Belize and Mexico in the first week of August, the Atlantic has now gone quiet.
(MORE: Dozens Killed by Earl in Mexico)
As of Thursday, the National Hurricane Center (NHC) indicated that no tropical depressions or tropical storms are forecast to develop in the Atlantic during the next five days. Global forecast models are also not showing any strong signals for development in the days ahead.
This is happening at a time of year when activity in the tropics is typically ramping up, though quiet periods during the August-September period are not uncommon.
So why are the tropics taking a breather right now?
For one, the Madden-Julian Oscillation, often referred to as the MJO by meteorologists, is located over the western Pacific Ocean. This is illustrated by the green shadings in the tweet below from Eric Blake, a hurricane specialist at the NHC.

Wherever the MJO is in place around the globe, there is typically rising air and storminess in the latitudes near the equator in that area. Those are some of the ingredients needed for the development of tropical depressions, tropical storms and hurricanes.
The MJO typically moves around the globe every 30 to 60 days, according to Dr. Jeff Masters of Weather Underground.
For the next week or two, forecast models are indicating that the MJO will stay over the western Pacific, Masters says. This means that there will be sinking air over the Atlantic basin and higher surface pressures, which are generally not favorable for the development of tropical systems.
In addition, there is also a good bit of dry and/or dusty air in the tropical Atlantic Ocean west of the African coast. This so-called Saharan Air Layer, or SAL, tends to squelch shower and thunderstorm activity associated with tropical waves moving from off the African coast westward through the Atlantic.

Orange and red shadings show where dry, dusty air was in place on Aug. 11, 2016. (UW-CIMSS/NOAA-HRD)

Tropical waves are sometimes seeds for the development tropical depressions, tropical storms and hurricanes.
Shower and thunderstorm activity must persist in association with the tropical waves in order to generate the closed circulation center needed for a tropical depression or storm to develop. Once that happens, they can develop further should other atmospheric conditions be favorable such as upper-level winds.
(MORE: Tropical Waves Explained)
While we are in a lull in activity in the Atlantic right now, the season is likely to pick up in the weeks ahead.
We are now in a time of year when the Atlantic has had some of its strongest hurricanes.
About 90 percent of the Atlantic's major hurricanes (Category 3-5) during the last 50 years have occurred after Aug. 10, according to Dr. Phil Klotzbach, a tropical scientist at Colorado State University.

MORE: Retired Atlantic Hurricane and Tropical Storm Names