While meteorologists continue to predict that the upcoming hurricane season, which officially starts Saturday, will be near normal to slightly below normal, some of the data supporting that prediction are changing, leading to the possibility of a more active season.
This points once again to the importance of preparing for a storm now, rather than waiting until one is on the horizon.
The National Oceanic and Atmospheric Administration predicted a 40 percent chance of a near normal season in its May 23 report, with nine to 15 named storms, four to eight of which could become hurricanes, including two to four major hurricanes.
Similarly, in its April report the Colorado State University Tropical Meteorology Project predicted a slightly-below-average season. CSU will update its forecast Tuesday.
Both the NOAA and CSU reports pointed to a weak El Niño system forming in the Pacific, which would cause wind shear in the Atlantic basin. High altitude wind shear tends to tear storms apart as they move across the Atlantic, preventing them from developing into hurricanes.
However, NOAA also pointed to above normal sea surface temperatures in the tropical Atlantic and Caribbean, which may serve to cancel out the impact of the El Niño.
“This outlook reflects competing climate factors. The ongoing El Niño is expected to persist and suppress the intensity of the hurricane season. Countering El Niño is the expected combination of warmer-than-average sea-surface temperatures in the tropical Atlantic Ocean and Caribbean Sea, and an enhanced West African monsoon, both of which favor increased hurricane activity,” the NOAA report noted.
This uncertainty adds gravity to the importance of hurricane preparation before a storm looms on the horizon.
“Preparing ahead of a disaster is the responsibility of all levels of government, the private sector, and the public,” said Daniel Kaniewski, FEMA’s deputy administrator for resilience. “It only takes one event to devastate a community so now is the time to prepare. Do you have cash on hand? Do you have adequate insurance, including flood insurance? Does your family have communication and evacuation plans? Stay tuned to your local news and download the FEMA app to get alerts, and make sure you heed any warnings issued by local officials.”
One named tropical weather system got a jump on the season when on May 20 subtropical storm Andrea spun up north of the Dominican Republic and several hundred miles southeast of Bermuda. The storm did not make landfall and petered out to the north northeast. But it was a reminder that tropical weather systems don’t necessarily behave by any rules and people in the tropics need to be ready for any eventuality.
Surface Temperatures Generally Warmer
The overall look of the ocean temperatures across the Atlantic is warmer now than at this time last year, records indicate. In particular, the central and eastern Atlantic between the coast of Africa and the Lesser Antilles (where storms develop) are above average.
Most of the seasonal models are projecting above average rainfall. In addition, the rainfall across the Sahel of western Africa has been above average this year and this can signal robust tropical disturbance activity from the coast of Africa. Given those factors, combined with the position of the upper level high pressure ridge, means there is a medium-high risk for a tropical storm or hurricane impact across the Leeward Islands, Virgin Islands, Puerto Rico, and the north coast of the Dominican Republic.
Sea surface temperatures between the west coast of Africa and the Lesser Antilles are generally warmer now than at this time last year. Also, increased doubt is being cast on whether the El Niño conditions will last through the summer and fall seasons, as the forecast suggests they will. In fact, some models project the El Niño to fade by August, September, and October, the high point of the hurricane season.
Hurricane forecasters also are keeping an eye on the persistent deep thunderstorm activity that has been occurring over the African continent during the last four to six months. Rainfall totals over the Sahel region of Africa have also been well above average this year. A strong western African monsoon season leads to stronger than average tropical waves and milder easterly trade winds. The slower-than-average trades have a tendency to limit not only Saharan dust volumes, but contribute to a low wind shear environment across both the eastern and central Atlantic.
The warmer ocean temperatures, doubts about the duration of El Niño conditions, persistent thunderstorm activity across western Africa, the potential for stronger tropical waves and milder trade winds are all signals that the hurricane season will likely be much more active that was originally projected just a few months ago.
Is Wind Shear a Vanishing Factor?
A report released by NOAA on Tuesday suggests that as the years pass, wind shear will become even less of a factor in the Atlantic Basin hurricane season.
New model simulations suggest that higher greenhouse gas emissions will reduce or even eliminate vertical wind shear along the U.S. East Coast by the end of the century.
“Active hurricane eras, such as the one we’ve been experiencing since the mid-1990s, tend to simultaneously produce relatively high vertical wind shear along the U.S. East Coast. This shear acts like a ‘speed bump’ to landfalling hurricanes, making them less likely to rapidly intensify before coming ashore,” according to NOAA’s report, authored by Rebecca Lindsey.
Vertical wind shear and water temperatures in the tropical North Atlantic are the two most important influences on seasonal hurricane activity. When conditions in the main hurricane development region are especially favorable for hurricane formation – meaning warm temperatures and low vertical wind shear – conditions are simultaneously less favorable over the East Coast. But that built-in protection may erode in the future, leaving the heavily populated East Coast more vulnerable to storms that rapidly intensify as they approach landfall.
The increase in potential intensity along the U.S. East Coast, coupled with the more favorable wind shear environment for hurricane intensification there, suggests that hurricanes tracking toward the U.S. East Coast will have a better chance of achieving their potential intensity in the future, which may be much stronger than what we’ve experienced in the past.