Researchers at the Colorado State University Tropical Meteorology Project have increased their forecast for the 2017 hurricane season, which began Thursday, calling for a “near average” season.
In an April prediction the forecasters were calling for a slightly below average, (See Related Links, below.) but a reduced likelihood of a moderate El Niño and recent anomalous warming in the tropical Atlantic caused them to increase their prediction.
In a news release issued Thursday, CSU predicted 13 additional named storms – Tropical Storm Arlene formed in April, so the forecast is for 14 total named storms this year.
Of those, researchers expect six to become hurricanes and two to reach major hurricane strength (Saffir/Simpson category 3, 4 or 5) with sustained winds of 111 miles per hour or greater.
In May, the National Oceanic and Atmospheric Administration predicted a slightly stronger than average season, with a 70 percent likelihood of 11 to 17 named storms, of which five to nine could become hurricanes (winds of 74 mph or higher), two to four of which will become major hurricanes.
An average season produces 12 named storms of which six become hurricanes, including three major hurricanes.
But as islanders know, the total number of storms isn’t the key. As the saying foes, it only takes one to ruin your whole day.
The weak La Niña that occurred last winter has dissipated, the forecast said, and while there is the potential that a weak El Niño could develop by the peak of the Atlantic hurricane season, the odds of a stronger El Niño event, which could hamper storm development, appear to have diminished.
El Niño conditions tend to increase upper-level westerly winds across the Caribbean into the tropical Atlantic, tearing apart hurricanes as they try to form, according to the CSU news release. The tropical Atlantic has warmed over the past two months and is now warmer than normal. In addition to providing more fuel for tropical cyclone formation and intensification, warmer tropical Atlantic sea surface temperatures are associated with a less stable atmosphere as well as moister air, both of which enhance organized thunderstorm activity necessary for hurricane development.
The far North Atlantic, however, remains colder than normal, potentially indicate of a negative phase of the Atlantic Multi-decadal Oscillation.
The Colorado team bases its forecasts on more than 60 years of historical data that include Atlantic sea surface temperatures, sea level pressures, vertical wind shear levels (the change in wind direction and speed with height in the atmosphere,) El Niño (warming of waters in the central and eastern tropical Pacific), and other factors.
So far, the 2017 hurricane season is exhibiting characteristics similar to 1957, 1969, 1979, and 2006, according to the report.
“1957, 1979 and 2006 had slightly below-average hurricane activity, while 1969 was a very active season,” said Phil Klotzbach, research scientist in the Department of Atmospheric Science and lead author of the report.
The CSU team will issue forecast updates on July 3 and August 4.
The CSU forecast is intended to provide a best estimate of activity to be experienced during the upcoming season – not an exact measure.
The report also included the probability of major hurricanes making landfall:
– 55 percent for the entire U.S. coastline (average for the last century is 52 percent;)
– 33 percent for the U.S. East Coast including the Florida peninsula (average for the last century is 31 percent;)
– 32 percent for the Gulf Coast from the Florida panhandle westward to Brownsville (average for the last century is 30 percent;)
– 44 percent for the Caribbean (average for the last century is 42 percent.)