I’ve written extensively in the past on why I think preseason tropical activity forecasts are generally fairly useless. And indeed, trying to specifically predict a particular number of storms is pretty silly. Although hurricane seasons are medium-period events, occupying the gray area between long-term weather and short-term climate, individual hurricanes are short-period events, influenced heavily by other short-period events, which are inherently chaotic and unpredictable. You could have perfect conditions for a busy season, yet a half-dozen or a dozen instances of right-place, right-time wind shear, for instance, can give you a below-average storm count. Conversely, a season that “should” be calm can end up “active” because micro-conditions happen to be “just right” for a bunch of storms and stormlets, despite hostile macro-conditions.
Moreover, and perhaps more importantly, preaseason forecasts tell us exactly nothing about what really matters to people, which is where storms will go, and what impact they’ll have. The 1992 hurricane season is the archetypal example: it was a “slow” season, yet it produced Hurricane Andrew. So, really, it wasn’t a “slow” season at all, practically speaking, at least not in a way that matters to anyone. “An active year is the year when you get hit,” as they say.
Having said all that… storm-filled seasons, strong hurricanes, and devastating land impacts are certainly statistically more likely if the macro-conditions are right. And, as we approach the “official” start of hurricane season on Tuesday, it appears the macro-conditions are just about perfect for an active season. Cue NOAA’s forecast:
An “active to extremely active” hurricane season is expected for the Atlantic Basin this year according to the seasonal outlook issued today by NOAA’s Climate Prediction Center – a division of the National Weather Service. …
Expected factors supporting this outlook are:
Upper atmospheric winds conducive for storms. Wind shear, which can tear apart storms, will be weaker since El Niño in the eastern Pacific has dissipated. Strong wind shear helped suppress storm development during the 2009 hurricane season.
Warm Atlantic Ocean water. Sea surface temperatures are expected to remain above average where storms often develop and move across the Atlantic. Record warm temperatures – up to four degrees Fahrenheit above average – are now present in this region.
High activity era continues. Since 1995, the tropical multi-decadal signal has brought favorable ocean and atmospheric conditions in sync, leading to more active hurricane seasons. Eight of the last 15 seasons rank in the top ten for the most named storms with 2005 in first place with 28 named storms.
NOAA is predicting 14 to 23 named storms, including 8 to 14 hurricanes, of which 3 to 7 could be major hurricanes. (Credit NOAA for giving a range, instead of a specific number. That’s much better.) Other predictions also call for an active season, though NOAA’s forecast appears to be the most bullish.
Blogger (and, FWIW, global warming denialist — I mention this only because I know it will come up in comments) Alan Sullivan, who often pooh-poohs alarmist storm predictions, is totally on board with this one, and has been for some time. Examples and analysis after the jump.
On April 7, he wrote:
Seasonal hurricane forecasts are emerging. It is early, of course, but I concur with the expectations of an active time — and possibly very active. I think the University of Colorado forecasters might be too conservative, but all depends on the manner and timing of El Nino’s demise. As we see from the Rio rains, El Nino patterns are still dominant. Three months from now, that could change. Already I see the building high pressure in the sub-tropical Atlantic, and the persistent easterly flow here, that presage trouble, as these conditions steer storms that do form toward North America, when the time comes. Watch out, Florida! I doubt the state will go unscathed this summer.
Then on April 24:
El Nino is weakening notably in the equatorial Pacific and cool anomalies are spreading over the rest of the immense basin. Negative phase of the Pacific decadal oscillation is reasserting itself. At present the most striking warm anomaly in the planet’s oceans is found across the tropical Atlantic into the Caribbean. This does not bode well for hurricane season. Be warned.
And on May 4:
The first TUTT (tropical upper tropospheric trough) of the coming season is coursing westward through the Caribbean … Hurricanes and TUTTs are closely associated, often travelling in tandem across the Atlantic. … It is ominous to see a TUTT active so early. …
There are other ominous signs for the Atlantic hurricane season. If you look at a map of current maritime temperature anomalies, you will see that the El Nino is fading rapidly. Cool blue covers almost the whole Pacific north of the equator. This will induce a favorable upper wind configuration. Meanwhile the warm anomaly in the tropical Atlantic has actually grown. Why? Because the northern polar jet continues abnormally far south in many parts of the world. It is suppressing the Atlantic subtropical high. Atlantic trades are weaker than usual, and skies are persistently clear from the equator to about latitude 25N. This is letting the strong May sun heat the waters more. … [T]his year the peril is clear, and it is time to prepare.
Early yesterday, before the NOAA forecast was released:
[T]he equatorial Pacific has lapsed almost overnight from fading El Nino to a rapidly chilling and spreading La Nina. We are about to see a convulsion in tropical weather everywhere. I fear that means a fusillade of hurricanes in the Atlantic. Indications grow stronger for that, as the Atlantic remains anomalously warm S of 30 N. That energy only awaits a trigger.
Finally, later yesterday, after the forecast came out:
I can confirm the new “official” hurricane forecast. Have I not been saying it myself for months? Yes, this will be a bad year, very bad. Commodity markets went crazy at once. They could have made more orderly adjustments, if they read FB!
“FB” means Alan’s blog, “Fresh Bilge.”
For my part, I suspect I’ll be too busy with fatherhood and lawyerhood to really do this season justice, 2005-style, if it is indeed a bad one. I’ll blog about hurricanes, no doubt; I can’t help myself. But I suspect it’ll be a lot more tweeting and short-form linking, and a lot less long-form analysis, than in the good ol’ days. I ain’t a 2L anymore.
P.S. I almost forgot: PANIC!!!!! 🙂
Pingback: Where are the hurricanes? Stay tuned — they’re coming | Sullivan's Travelers