Does early start indicate start of violent hurricane season?
Friday, June 1, 2018, 16:25 - The Atlantic hurricane season is officially underway and understandably many are concerned about a repeat of last year’s hyperactive and devastating season, especially since we have already had our first named storm of the year (Alberto) make landfall before the official start of the season.
However, there is some good news as we look ahead at the upcoming season. First, having a storm develop during May is not a precursor to an active season. Since 1950, there have been 14 years with a named storm in the Atlantic Basin during the month of May and most of those year went on to have near normal or below normal tropical activity.
Also, the ocean water temperature pattern in the Atlantic Basin is very different right now from what we saw throughout the season last year, which also suggests that this year will be a much quieter season than last year.
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The two maps below compare current ocean temperatures versus this time last year. The various shades of red indicate warmer than normal water temperatures while the various shades of blue indicate cooler than normal water. The magenta colored rectangles highlight the “Main Development Region” (MDR) which is where the majority of tropical storms and hurricanes develop.
This time last year this region was warmer than normal and this pattern continued through the hurricane season. While there were other factors that contributed to the severity of the last year’s hurricane season, warmer than normal ocean water did contribute to the intensity of the storms.
However, not only is this region several degrees cooler than last year, it is cooler than it has been since 1994. While the pattern could change between now and the heart of the hurricane season (mid-August through September), we expect that this region will remain cooler than normal for the next few months.
The cooler ocean water temperatures in the tropics also gives us an environment that is less favorable for the development and intensification of tropical storms and hurricanes. In addition, the large region of much warmer than normal water to the north also contributes to a pattern that is less favourable for the development of storms in the tropics.
The current pattern creates a set up in which the air tends to sink over the tropics, resulting in higher surface pressure and diverging surface winds. This is opposite to the pattern that would enhance the development of tropical storms and hurricanes (lower surface pressure, rising air and converging surface winds).
Because of these factors, we think it is more likely to see the lower end of the forecast ranges given by the National Hurricane Center for the upcoming season.
WHY EAST OF COAST CANADA AND U.S. SHOULD BE ON GUARD
Despite having a pattern that favours less development of hurricanes compared to last year, those along the East Coast of the U.S. and Atlantic Canada should not let their guard down. While forecasts for the hurricane season often focus on the number of storms, the impact of the season is based on whether any storms come ashore and the intensity of the storms when they do hit land. Remember, it only takes ONE major hurricane to make for a memorable season.
Unfortunately, the warmer than normal water in the Atlantic Basin is found in close proximity to the Eastern Seaboard of the U.S. and south of the Maritime provinces of Canada. This is a concern because it could give those regions a pattern that is more favorable for the development of a tropical system close to the coast -- and storms that do develop close to the coast are generally more likely to make landfall than those which form in the central or eastern Atlantic.
Also, if a storm does approach the coast of the U.S. or Canada, it would have more of an opportunity to maintain strength over the relatively warm water.
All in wall, while we expect a much quieter season than last year with a much lower risk for long tracked major hurricanes, the threat is still there for a storm or two that could have a major impact to the coast of the U.S. and/or Canada.