Record ocean temperatures and La Nina signal ‘extraordinary’ Atlantic hurricane season

The 2024 Atlantic hurricane season is expected to be significantly more active than usual, with NOAA predicting 17 to 25 named storms, 8 to 13 hurricanes, and 4 to 7 major hurricanes. The North Atlantic hurricane season runs from early June to late November.

• This is NOAA’s highest prediction for Atlantic hurricane season since federal hurricane outlooks began in 1999.
• La Nina will likely develop between July and September 2024 and persist through the Northern Hemisphere winter.

NOAA’s 2024 Atlantic hurricane season forecast — released Thursday, May 23, highlights several contributing factors to the expected increased activity. Near-record warm ocean temperatures in the Atlantic Ocean, the development of La Nina conditions in the Pacific, reduced Atlantic trade winds, and less wind shear all favor the formation of tropical storms.

The forecast follows one of the strongest El Ninos ever observed, with a predicted transition to La Nina conditions, which are conducive to Atlantic hurricane activity due to reduced wind shear. At the same time, high sea surface temperatures in the tropical Atlantic Ocean and Caribbean Sea will provide more energy for storm development.

Additionally, an above-normal west African monsoon also has the potential to generate African easterly waves, seeding strong and long-lived Atlantic storms.

Regarding La Nina prediction, NOAA’s Climate Prediction Center (CPC) reported below-average sea surface temperatures (SSTs) in parts of the eastern Pacific Ocean in April 2024, while the rest of the equatorial Pacific experienced above-average SSTs.

The latest weekly Niño index values remained between +0.5°C and +0.8°C in all regions, except for Niño-3 which was +0.3°C. Below-average subsurface temperatures held steady during the month, with negative anomalies extending from the Date Line to the eastern Pacific Ocean. Low-level wind anomalies were easterly over the western equatorial Pacific, while upper-level winds were near average. Convection was near average overall across the equatorial Pacific Ocean and Indonesia.

This pattern reflects the ongoing weakening of El Niño and a transition toward ENSO-neutral conditions.

Forecast models predict an imminent transition to ENSO-neutral, with La Nina likely developing between July and September 2024 and persisting through the Northern Hemisphere winter.

CPC forecast team favors model guidance suggesting La Nina could form as early as June-August 2024, with a 49% chance in June-August and a 69% chance in July-September.

“NOAA’s forecast comes as tropical Atlantic waters reach all-time records for the time of year,” said Michael Lowry of Eye on the Tropics.

“As of this week, 92% of the Main Development Region of the Atlantic – where 85% of Category 3, 4, and 5 hurricanes form – is at record or near-record seasonal warmth.”

“This season is looking to be an extraordinary one in a number of ways,” NOAA Administrator Dr. Rick Spinrad said. “The forecast for named storms — hurricanes and major hurricanes — is the highest NOAA has ever issued for the May outlook.”

“Severe weather and emergencies can happen at any moment, which is why individuals and communities need to be prepared today,” FEMA Deputy Administrator Erik A. Hooks said.

National Weather Service (NWS) Director Ken Graham noted that the seasonal outlook is a reason for concern but not alarm. He reminded coastal residents that hurricane preparedness is crucial, as even tropical storms can intensify rapidly before landfall.

NOAA’s strong outlook aligns with similar forecasts from other organizations, such as Colorado State University, which issued its highest seasonal predictions to date in early April.

To enhance communication and decision support during the 2024 season, NOAA will implement several improvements:

• Expansion of Spanish language text products to include all Public Advisories, Tropical Cyclone Discussion, Tropical Cyclone Update, and Key Messages in the Atlantic basin.
• An experimental version of the forecast cone graphic to include inland tropical storm and hurricane watches and warnings in effect for the continental U.S., starting on or around August 15.
• Issuance of U.S. tropical cyclone watches and warnings with regular or intermediate public advisories.

New forecast models developed by NOAA researchers, such as the Modular Ocean Model (MOM6) and SDCON, will improve the prediction of hurricane intensity and the probability of rapid intensification.

NOAA’s new generation of Flood Inundation Mapping will provide vital information to emergency and water managers for better preparation and response to potential flooding.

Observational system upgrades include enhanced coastal weather buoys and the deployment of Directional Wave Spectra Drifters (DWSDs) and Saildrones. Additionally, dozens of observational underwater gliders will be deployed off the Caribbean, the Gulf of Mexico, and the eastern U.S. coast.

NOAA’s CHAOS research experiment aims to improve understanding of air-sea interactions, contributing to better hurricane monitoring and forecasting.

Updates to the 2024 Atlantic seasonal outlook will be issued in early August, before the historical peak of the season.

References:

¹ NOAA predicts above-normal 2024 Atlantic hurricane season – NOAA – May 23, 2024

² Government Forecasters Issue their Highest Hurricane Season Outlook to Date – Eye on the Tropics – May 23, 2024

³ EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION – NWS/CPC – May 9, 2024

Featured image: Hurricanes Idalia and Franklin on August 29, 2023. Credit: NOAA/GOES-East