Tropical Storm Ana as viewed from the International Space Station, May, 2015 (Terry Virt via Twitter)
Tropical Storm Ana as viewed from the International Space Station, May, 2015 (Terry Virt via Twitter)

In three of the last 8 years, named tropical storms have formed in the Atlantic basin before the “official” start of hurricane season, defined as June 1. Just in the past week, Tropical Storm Ana formed off the Southeast coast and came ashore near Myrtle Beach as the second earliest U.S. landfalling tropical storm on record (Sunday).

Marshall Shepherd, a past president of the American Meteorological Society, recently posed the question: Should the start of hurricane season be moved to May 1, in light of recent “pre-season” activity?

I decided to put this question in front of the National Hurricane Center, which sets the boundaries for hurricane season. James Franklin, the branch chief for the Hurricane Specialist Unit, emailed me a detailed response explaining that May tropical storms and hurricanes in the Atlantic  are unusual enough that he believes the June 1 start date still makes the most sense.

“On balance, I think the ‘official’ hurricane season is starting more or less in the right place, and I don’t see much benefit to moving it up,” Franklin said. “The National Hurricane Center database shows only 23 named storms occurring in the month of May since 1851, and in the satellite era [since the early 1970s] we have had a named storm only about once every six years. So May storms are relatively rare occurrences.”

Franklin said changing the start date would tax the Center’s staffing and interfere with “preseason work”:

We could move up the start date to May 15 without a major impact on staffing, since we already begin our forecast shifts on that date with the start of the eastern North Pacific season. However, starting the season earlier than May 15 would have costs in terms of increased salaries as well as lost productivity on the part of the forecasters, who, when they’re not working forecast shifts are engaged in research and development projects, outreach and training, and other activities. The outreach and training season is an extremely busy and productive time for us, so we’d hate to pull the forecasters away from that activity to mostly be writing empty Tropical Weather Outlooks.

Similarly, moving the start day earlier than May 15 would reduce the time available for off-season technical development. This year, for example, we were working on formatting changes to the Public Advisory and introduction of a storm surge watch/warning graphic. (And we’re still working on the finishing touches of the surge graphic generation.) These development efforts currently get targeted with either June 1 or May 15 implementation dates depending on the basin and the nature of the development.

In addition, Franklin worries having hurricane season start too long before the peak of the season – typically in August and September – may lull in the public into a false sense of security or lead to complacency in years with little action May through July.

“I’m already concerned that we have our major preparedness media push too far removed from the peak of the season,” Franklin said. “Around June 1, the season opens to much fanfare, and then in most years nothing much happens until August. If the season began in early or mid-May, I’d be concerned that our preparedness message would be less effective.”

Brian McNoldy, Capital Weather Gang’s tropical weather expert, agrees with Franklin. “There aren’t really any good arguments for moving the official start of hurricane season into May,” he said.

Three times as many storms have formed in November, the final month of hurricane season, compared to May over the last 50 years, McNoldy said. He added the median dates for the first named tropical storm and first hurricane are a long time after May 1: June 23 and August 6, respectively.

Only one hurricane on record has formed prior to June 1 in the satellite era, McNoldy said. And the Hurricane Center’s Franklin noted that one hurricane didn’t strike land. “So from an impacts perspective, there doesn’t seem to be a pressing need to get folks’ attention any earlier,” Franklin said.

Shepherd said when he posed the question, he was simply “being provocative” and wasn’t advocating an earlier start date. But he cautioned we shouldn’t dismiss the impacts pre-season tropical storms can have and should consider whether me might start seeing more. “[They] can be the most significant rain producers so their presence/frequency is not trivial,” he said.

A 2008 study in Geophysical Research Letters found some preliminary evidence for a lengthening Atlantic hurricane season, including more pre-season storms, but noted “high uncertainty.”

McNoldy said data he’s analyzed show a trend towards an earlier average date of the first tropical storm but, on the flip side, the average date of the first hurricane has trended later.


(Brian McNoldy)

(Brian McNoldy)

By increasing year-round ocean temperatures that fuel tropical storm activity, it’s possible climate warming could – over time – extend (or continue extending) the season in which we see tropical activity. So even if the goal posts for hurricane season remain static for now, this question of whether hurricane season should be amended may re-emerge in the future.