Blog: Hurricane season is less than a month away - a look at competing factors in this year’s forecast
Record sea surface temperatures and El Niño
NEW ORLEANS (WVUE) - The start of June marks the beginning of the Atlantic hurricane season.
With less than one month to go, all eyes are turning to this year’s forecast. Colorado State University released its 2023 hurricane season outlook last month, predicting a slightly below-normal season with 13 named storms, 6 hurricanes, and 2 major hurricanes. The average tropical season for the period between 1991 and 2020 is 14.4 named storms, 7.2 hurricanes, and 3.2 major hurricanes.
Different factors contribute to the Atlantic hurricane season forecast each year.
Sea Surface Temperatures
The warmth of the waters in the tropical North Atlantic Ocean is known to influence the formation of tropical systems. Warmer waters create conditions more favorable for hurricanes to form.
Tropical cyclones are fueled by latent and sensible heat fluxes, which are increased by warmer waters. Latent heat flux is the transfer of heat between the Earth’s surface and the atmosphere. It is associated with water evaporation at the surface and condensation of water vapor in the lower troposphere, the bottom layer of the atmosphere. Sensible heat flux is the transfer of heat between the earth’s surface and atmosphere as well, but it is the heat that is not associated with phase changes of water. The release of heat and the addition of water to the atmosphere help to fuel hurricanes.
Lower pressure and reduced low-level trade winds have also been noted with warmer waters, creating a better environment for hurricane formation. As pressure drops, winds are sucked into the center of a hurricane faster leading to increasing wind speeds. Vertical wind shear tears hurricanes apart, therefore reducing this variable allows for enhanced tropical formation.
Sea surface temperatures (SST) are an important factor in hurricane forecasting. Hurricanes are fueled by warm air and warm seawater, so they typically form over tropical oceans where SSTs are higher. Increased rising motion is found in the areas where SSTs are anomalously warm, favoring enhanced tropical activity.
The 30-day average SSTs in the eastern North Atlantic are currently the warmest on record according to CSU meteorologist Phil Klotzbach. The current temperatures rank just ahead of 2010 for the warmest years. The top five warmest years of SSTs are 2023, 2010, 2020, 1998, and 2005. Every year had an above-average hurricane season except for 1998, which had an average hurricane season of 14 storms. The record number of storms was set in 2020 with 30 storms, and 2005 followed close behind with 27 named storms.
These anomalously warm SSTs will be competing with the transitioning El Niño-Southern Oscillation (ENSO) cycle.
Transition to El Niño
The ENSO is a recurring climate pattern that involves changes in the temperature of water in the central and eastern tropical Pacific Ocean. The surface waters in this region are warming or cooling for a period ranging from about three to seven years. The oscillating pattern affects rainfall distribution in the tropics and influences weather patterns worldwide and in the United States.
According to an update from the WMO on May 3, there is a 60% chance for a transition from ENSO-neutral to El Niño from May to July 2023. This will increase to 70% from June to August, then to 80% between July and September.
El Niño is typically associated with slower hurricane seasons in the Atlantic. During El Niño, vertical wind shear is increased over the Atlantic leading to decreased tropical cyclone activity.
During the upcoming hurricane season, the record-warm SSTs and transition to El Niño will be competing. Forecasts are leaning toward El Niño driving the activity to be slightly lower, but it only takes one storm to make it a bad hurricane season for southeastern Louisiana and the northern Gulf Coast. Take the time to prepare in advance regardless of the hurricane season forecast.
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