The peak of the Atlantic hurricane season passed us by last week… and you may have noticed that overall, the season has been somewhat quiet (even though things seem to be shifting, but more on that below).
There have been seven named storms so far – including Francine, which brought heavy rains and storm surge to Louisiana before moving inland last week. Gordon also formed late last week in the Atlantic.
While the season will continue into November, that total of named storms is pretty far below the totals projected by NOAA earlier this year. Back in May, the agency was predicting an above-average year, with anywhere from 17 to 25 named storms.
Stephanie Zick is a hurricane expert at Virginia Tech, and she says one reason for that above-average projection is still very much present.
“We have above-average sea-surface temperatures broadly across the Atlantic. Really above-average sea-surface temperatures – record-breaking – depending on the area that you’re averaging over. So, this is potentially the hottest Atlantic Ocean we have seen on record.”
That super warm water acts as a sort of fuel source for tropical systems. Zick adds that NOAA and other forecasters were also factoring in the phase of ENSO – or the El Nino Southern Oscillation – into that original projection.
“At the time, I think it was El Nino, transitioning to neutral and we are anticipating this will develop into a La Nina. So, that kind of neutral-La Nina phase tends to favor more tropical cyclones.”
The season got off to a quick start with Beryl, Zick says, which had one of the earliest rapid intensifications on record – but then things kind of slowed down in mid-August, which is when you’d expect to have a flurry of activity.
So, what gives? What caused that drop off? Zick says there are a few theories...
- An active African monsoon season: Zick says the active, wet monsoon season in Africa has pushed an easterly jet further north than average. So, waves that could become tropical systems moved off that continent into the Atlantic further north, where conditions for development aren’t as good. She says the jet does appear to moving back to its normal position, so more development of tropical systems could be on the horizon.
- Unfavorable shear environment: Remember, wind shear is the change of wind speed or direction as you move up in the atmosphere. High wind shear at certain points in the atmosphere will stymie the development of tropical storms and hurricanes, Zick says. “We’ve had really, really strong easterly winds in the upper atmosphere – up near what we call the tropopause. And this is an easterly jet associated with the Indian monsoon. So, potentially these waves are moving off into a dry environment with a little bit higher shear – and so they’re just dying and dissipating.
- A phase of something called the Madden-Julian Oscillation: The MJO is a recurring climate pattern – similar to El Nino – which Zick says certain phases of can either lead to suppressed or enhanced conditions for precipitation in the Atlantic. She adds we’ve been in the phase that suppresses rainfall – again affecting hurricane development – but that also seems to be changing.
Long story short, there have been a number of factors keeping tropical development from really popping off this year. But conditions do seem to be shifting more towards the favorable side for that development.
Zick says it’s incredibly difficult to predict what the hurricane season will look like in October and November during the spring – which is when most of the initial season projections come out.
She adds we still have some time left, too.
“We’ve got half of [the season] left. And I do expect this season to be above-average still.”
As this newsletter was being compiled late last week, the National Hurricane Center was tracking Francine, and as I mentioned above, Gordon also formed late in the week. Things could change even further this week, with some models showing (as of last Friday afternoon) some tropical development that could impact Virginia this week. Time will tell if those projections play out after all.
Taking a look at meteorological fall...
It’s now officially meteorological fall, y'all – so let’s take a look at what the National Weather Service’s Climate Prediction Center is thinking for the next few months.
The latest three-month projections from the CPC show all of Virginia having a good chance of being above average for temperatures. To give you an idea of what that would mean – the average daily high temperature for Blacksburg is just over 76 degrees Fahrenheit for September, 66 for October and 55 for November.
For precipitation, areas along and east of the Blue Ridge have anywhere from a 33-50% chance of seeing higher than normal precip totals – according to the CPC projection. Let’s use Lynchburg this time – the average precipitation total for September is 3.56 inches, 3.30 inches for October and 3.36 for November.
Any rainfall in the near future would be welcomed – as the latest U.S. Drought Monitor has most of Virginia under some level of dryness or drought right now. That includes severe drought for parts of the Shenandoah Valley.
Thanks for checking out this edition of CommonWx — the weather and climate newsletter from Radio IQ. Use this link to get the newsletter sent to your inbox.
