Tropical Storm Arlene spins up in the Atlantic, two months before average date of first storm of hurricane season

By Tom Yulsman | April 21, 2017 9:25 pm

Is climate change playing any role in an apparent lengthening of the hurricane season?

Tropical Storm Arlene

Arlene, as seen by NASA’s Terra satellite on the morning of Friday, April 21, 2017 — probably before it was downgraded in status from a tropical storm. The U.S. East Coast is off screen to the left. (Source: NASA Worldview)

It’s way early for hurricane season to start, but that’s precisely what happened yesterday with the formation of Tropical Storm Arlene in the far northern Atlantic.

Brian McNoldy, a researcher at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, writing at his Tropical Atlantic Update blog, puts this into perspective:

. . . this is exactly two months before the average date of first storm formation (June 20). It is also the 6th pre-season named storm to form in the past 6 years.

And as Weather Underground meteorologist Brian Henson put it in a post today:

Getting a tropical or subtropical depression in the Atlantic in April is about a once-per-decade event, and a tropical storm in April is even more unusual. The NOAA Historical Hurricane Tracks website shows that only four April tropical or subtropical depressions are known to have formed in in the Atlantic prior to Arlene, although many such systems would have gone undetected prior to the advent of routine satellite monitoring in the 1970s.

Arlene did not stay at tropical storm strength for long. The National Hurricane Center declared it a tropical storm at 5 p.m. on Thursday. And by 11 a.m. on Friday, it had downgraded the storm.

But Arlene does not appear to be a quirk. From the mid-1960s at least, there appears to be a trend of earlier and earlier first Atlantic named storms:

A study back in 2008 found evidence that the North Atlantic Hurricane season was getting longer, possibly due to a warming climate. Writing in the journal Geophysical Research Letters, James P. Kossin of the University of Wisconsin, Madison, concluded:

I find an apparent tendency toward more common early- and late-season storms that correlates with warming SST, but the uncertainty in these relationships is high.

“SST” means “sea surface temperatures,” and warm waters do indeed fuel storms. So it’s logical that warmer waters forming earlier in the season, and lingering later as well, could lengthen the hurricane season. But Kossin offered a big caveat:

The relationship with SST is suggestive of a larger link to climate variability, but no explicit link to human-induced global warming can be inferred from this study.

Atlantic hurricanes have been changing in multiple ways. The 2014 U.S. National Climate Assessment concluded:

There has been a substantial increase in most measures of Atlantic hurricane activity since the early 1980s, the period during which high-quality satellite data are available. These include measures of intensity, frequency, and duration as well as the number of strongest (Category 4 and 5) storms . . . However, there is considerable uncertainty in the record prior to the satellite era (early 1970s), and the further back in time one goes, the more uncertain the record becomes.

These changes, too, are linked to warming ocean waters. And the report noted that warming from human emissions of heat-trapping greenhouse gases was likely playing a role. But how much of a role compared to natural variability was then, and is still, a matter of scientific debate.

  • OWilson

    A tempest in a teapot?

    No more than a brief overnight squall, and it is linked to Global Warming?

    And, no, it did NOT “Start the Hurricane Season” :) In the North Atlantic, that begins June 1, as always.

    The old studies you quote from 2008 (“found evidence that the North Atlantic Hurricane season was getting longer, possibly due to a warming climate”) and 2014, have long since been surpassed by newer findings from The University of Colorado, among others :)

    “”Abstract – Ten years ago, Webster et al. documented a large and significant increase in both the number as well as the percentage of category 4 and 5 hurricanes for all global basins from 1970 to 2004,…. In contrast to that study, as shown here, the global frequency of category 4 and 5 hurricanes has shown a small, insignificant downward trend while the percentage of category 4 and 5 hurricanes has shown a small, insignificant upward trend between 1990 and 2014. Accumulated cyclone energy globally has experienced a large and significant downward trend during the same period. The primary reason for the INCREASE in category 4 and 5 hurricanes noted in observational datasets from 1970 to 2004 by Webster et al. is CONCLUDED TO BE DUE TO OBSERVATIONAL IMPROVEMENTS AT THE VARIOUS GLOBAL TROPICAL CYCLONE WARNING CENTERS, PRIMARILY IN THE FIRST TWO DECADES OF THAT STUDY.

    Klotzbach and Landsea, 2015

    Here’s their up to date forecast!

    “We anticipate that the 2017 Atlantic basin hurricane season will have slightly below average activity. The current neutral ENSO is likely to transition to either weak or moderate El Niño conditions by the peak of the Atlantic hurricane season. The tropical Atlantic has anomalously cooled over the past month and the far North Atlantic is relatively cold, potentially indicative of a negative phase of the Atlantic Multi-Decadal
    Oscillation. We anticipate a below-average probability for major hurricanes makinglandfall along the United States coastline and in the Caribbean”

    • aka darrell

      “…Hurricane Season” in the North Atlantic. That begins June 1, as always.” Did anyone tell the hurricanes? Perhaps they don’t know.

      • OWilson

        Your government has decreed June 1 to November 30, as Hurricane Season.

        The government is important! :)

        • Tom Yulsman

          You are displaying increasing signs of nihilism.

    • Tom Yulsman

      A classic case of hearing only what you are primed to hear, and reading without actually perceiving what the words say. It’s an oddly interesting but also ultimately disturbing phenomenon to behold.

      • OWilson

        I appreciate the opportunity to provide the minority view, of mutually observed facts.

        I don’t think that should disturb anyone participating in a science blog.

        It is usually dismissed with an insult, anyway! :)

        • Mike Richardson

          You’d probably get more sympathy if you weren’t so quick with the insults yourself anytime someone makes the mistake of disagreeing with your “minority view” more than once. Now the fact-based view, as described in the article, is that the storm season was originally defined by historical averages. However, climate change means those averages are just that — history. Another disturbing phenomenon to behold.

          • OWilson

            I don’t need your “sympathy”, or your group hugs. My sky is not always falling.

            But, thanks anyway! :)



ImaGeo is a visual blog focusing on the intersection of imagery, imagination and Earth. It focuses on spectacular visuals related to the science of our planet, with an emphasis (although not an exclusive one) on the unfolding Anthropocene Epoch.

About Tom Yulsman

Tom Yulsman is Director of the Center for Environmental Journalism and a Professor of Journalism at the University of Colorado, Boulder. He also continues to work as a science and environmental journalist with more than 30 years of experience producing content for major publications. His work has appeared in the New York Times, Washington Post, Audubon, Climate Central, Columbia Journalism Review, Discover, Nieman Reports, and many other publications. He has held a variety of editorial positions over the years, including a stint as editor-in-chief of Earth magazine. Yulsman has written one book: Origins: the Quest for Our Cosmic Roots, published by the Institute of Physics in 2003.


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