The 2017 north Atlantic tropical storm season officially started on June 1. Predictions from NOAA, the USA’s National Oceanic and Atmospheric Administration, indicate conditions are more favourable for storm formation than for the past few years, with the exception of 2016, which was the most active since 2012, having 15 named storms, including seven hurricanes. This compares to a long term average of 12 named storms, including six hurricanes, of which three are typically major hurricanes.
For 2017 forecasters predict a 45 per cent chance of an above-normal season, a 35 per cent chance of a near-normal season, and only a 20 per cent chance of a below-normal season. As a result, between 11-17 named storms are expected, of which five to nine are liable to reach hurricane strength with mean wind speeds above 63 knots. Of these, two to four could reach category three status, with sustained wind speeds of more than 100 knots.
Tropical Storm Arlene created winds of up to 50mph a full six weeks before the official start of the Atlantic storm season.
The season’s forecast was updated on May 25 to reflect the expected lack of El Nino activity in the Pacific Ocean, which tends to reduce wind sheer in the Atlantic, along with warmer sea temperatures, which also helps the formation of tropical storms. “The outlook reflects our expectation of a weak or non-existent El Nino, near- or above-average sea-surface temperatures across the tropical Atlantic Ocean and Caribbean Sea, and average or weaker-than-average vertical wind shear in that same region,” says Gerry Bell, lead seasonal hurricane forecaster with NOAA’s Climate Prediction Center.
The 2017 season effectively got off to an early start, thanks to Tropical Storm Arlene, which formed in April. It’s exceptional for a storm to form so far north at any time of year, especially over relatively cool water so soon after winter, and for it to develop the structure of a tropical storm.
NOAA will update the outlook in early August, just before the peak of the season. The Atlantic season reaches its peak in September, when one storm, each week can be expected to form, and officially ends on November 30. According to NOAA the climate models are currently showing more uncertainty than usual, which is reflected in the comparable probabilities for an above-normal and near-normal season.