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Hurricane Season: CSU Team Decreases Forecast, Expects Near-Average Activity

This NOAA satellite photo from September 2017 shows Hurricane Irma, over the Turks and Caicos, with Hurricane Jose to the right. Jose missed the islands, but was followed by Maria, which was a destructive Cat 5. Tropical Storm Katia is far left, in the Gulf of Mexico.
This NOAA satellite photo from September 2017 shows Hurricane Irma, over the Turks and Caicos, with Hurricane Jose to the right. Jose missed the islands, but was followed by Maria, which was a destructive Cat 5. Tropical Storm Katia is far left, in the Gulf of Mexico.

Unexpected cooling in the Atlantic basin has prompted Colorado State University hurricane researchers to decrease their forecast for the hurricane season, which starts Friday.

In their final forecast (which can be seen here) before the start of the season, the CSU Tropical Meteorology Project team predicted a near-average season, with 13 additional named storms (Subtropical Storm Alberto jumped the gun, forming a week ago in the Gulf of Mexico and dropping a lot of ran on Florida.) Of those, the researchers expect six to become hurricanes and two to reach major hurricane strength (Saffir/Simpson category 3-4-5) with sustained winds of 111 miles per hour or greater. Including Subtropical Storm Alberto, the forecast is for 14 total named storms in 2018.

In April, the meteorologists had called for a “slightly above average” 2018 hurricane season.

Last year the CSU team had predicted an average season, and that forecast held true until September, when all hell broke loose in the Caribbean and the islands were hit by a pair of Category 5 storms. So keep that in mind when planning.

Anomalous Cooling in Atlantic

The primary reason for the decrease is “anomalous cooling in the tropical Atlantic,” the CSU news release said.

The weak La Niña that occurred last winter has dissipated, according to the CSU team, and there is the potential that a weak El Niño could develop by the peak of the Atlantic hurricane season – August through October. However, the forecast team believes that neutral ENSO (El Niño-Southern Oscillation) conditions are the most likely scenario for this year’s season. El Niño tends to increase upper-level westerly winds across the Caribbean into the tropical Atlantic, tearing apart hurricanes as they try to form.

The tropical Atlantic has cooled over the past two months and is now colder than normal, the CSU forecast reports. In addition to providing less fuel for tropical cyclone formation and intensification, cooler tropical Atlantic sea surface temperatures are associated with a more stable atmosphere as well as drier air, both of which suppress organized thunderstorm activity necessary for hurricane development.

The far North Atlantic also remains colder than normal, potentially indicative of a negative phase of the Atlantic Multi-decadal Oscillation.

Forecast Based on Historical Data

The team bases its forecasts on over 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 2018 hurricane season is exhibiting characteristics similar to 1986, 2001, 2012, and 2014. “1986 and 2014 were below-average hurricane seasons, while 2001 and 2012 had above-average activity,” said Phil Klotzbach, research scientist in the Department of Atmospheric Science and lead author of the report.

The team predicts that 2018 hurricane activity will be about 100 percent of the average season. By comparison, the extremely active 2017 season was about 245 percent of the average season.

The CSU team will issue forecast updates on July 2 and August 2.

The CSU forecast is intended to provide a best estimate of activity to be experienced during the upcoming season – not an exact measure.

Probability of Landfall

The report also includes the probability of major hurricanes making landfall:

41 percent for the Caribbean (average for the last century is 42 percent)
51 percent for the entire U.S. coastline (average for the last century is 52 percent)
30 percent for the U.S. East Coast including the Florida peninsula (average for the last century is 31 percent)
29 percent for the Gulf Coast from the Florida panhandle westward to Brownsville (average for the last century is 30 percent)

Storm Names for 2018

The names selected for the 2018 hurricane season are:
Alberto (Used May 26 for a storm in the Gulf of Mexico)
Beryl
Chris
Debby
Ernesto
Florence
Gordon
Helene
Issac
Joyce
Kirk
Leslie
Michael
Nadine
Oscar
Patty
Rafael
Sarah
Tony
Valerie
William

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