The 2017 Atlantic hurricane season is already one for the record books. The report card for September is particularly remarkable:
ABNT30 KNHC 011150
TWSAT
Monthly Tropical Weather Summary
NWS National Hurricane Center Miami FL
800 AM EDT Sun Oct 1 2017
For the North Atlantic...Caribbean Sea and the Gulf of Mexico:
The North Atlantic basin was extremely active in September. Four
tropical cyclones formed, all of which became hurricanes, and three
of those four became major hurricanes. Hurricane Irma was also
present in the basin as a major hurricane during the month, although
it formed in late August. Both Irma and Maria reached category 5
intensity during the month of September.
Based on a 30-year climatology (1981-2010), the number of named
storms forming in the basin during September was near average, but
the numbers of hurricanes and major hurricanes were both well above
average. In terms of the Accumulated Cyclone Energy (ACE), which
measures the combined strength and duration of tropical storms and
hurricanes, September 2017 was the most active month on record,
easily breaking the previous record of September 2004. Overall,
this September was about 3.5 times more active than an average
September from 1981-2010.
From a seasonal perspective, activity in the Atlantic basin so far
in 2017 is well above average, and this season is the 3rd most
active on record to date in the basin, behind 1933 and 2004.
Reports on individual cyclones, when completed, are available at
the National Hurricane Center website at
www.hurricanes.gov/data/tcr/index.php?season=2017&basin=atl .
Summary Table
Name Dates Max Wind (mph)
---------------------------------------------------
TS Arlene 19-21 Apr 50*
TS Bret 19-20 Jun 45
TS Cindy 20-23 Jun 60
TD Four 6- 7 Jul 30
TS Don 17-18 Jul 50
TS Emily 31 Jul- 1 Aug 45
H Franklin 6-10 Aug 85
H Gert 13-17 Aug 105
MH Harvey 17 Aug- 1 Sep 130
MH Irma 30 Aug-12 Sep 185
MH Jose 5-22 Sep 155
H Katia 5- 9 Sep 105
MH Lee 15-30 Sep 115
MH Maria 16-30 Sep 175
---------------------------------------------------
* Denotes a storm for which the post-storm analysis is complete.
$$
Hurricane Specialist Unit
For the first time in recorded history, we’ve had three United States landfalls of category 4 or stronger hurricanes in Texas, Florida and Puerto Rico. The previous record was one. The leeward islands suffered two direct impacts of category 5 hurricanes Irma and Maria. Irma set the all-time global record for sustained category 5 intensity. I could go on and on with the records this season has already broken.
Lately, we’ve had a much-needed respite from worrying about activity in the tropics. But the season is far from over. And in October, the focus shifts from the central Atlantic to the western Caribbean.
Here’s the history of tropical storm formation in early October:
and mid October:
While there’s still a fair number of storms that formed out in the Atlantic, they tend not to get as intense as September storms and they tend not to make it as far west.
That’s the good news. The less good news is that there’s a sort of fall mini-season in the western Caribbean which is of concern to the Yucatan, Central America, the northern Gulf Coast and especially western Cuba and Florida.
And right on cue, the global weather models are hinting at dropping pressures in the western Caribbean and possible development of an area currently north of Panama over the next several days. This is still a highly uncertain forecast but it’s looking likely that we’ll get our first storm of the October mini-season this weekend in the Gulf.
There’s good reason not to be too worried about this particular system yet — the current circulation is very broad and disorganized and there’s some very strong shear in the Gulf at the moment. That said, here’s what has me paying strong attention to this and any subsequent W. Caribbean development this fall:
The map above shows the tropical cyclone heat potential (TCHP) in the Caribbean as of yesterday. TCHP is a measure of the amount of heat available in the surface layers of the ocean for fueling cyclone strengthening. Anything above about 80 on the TCHP scale is plenty for intensifying a storm to major status.
Now compare the map above with this one from October 15, 2005 — three days before Hurricane Wilma formed in that region:
Just three days after the date of that map, Hurricane Wilma went from category 1 to category 5 dropping nearly 100 millibars in less than 24 hours over those warm waters just east of the Yucatan. But those waters were nowhere near as warm as what we have this year. Not even close.
That doesn’t mean we’re going to have another Wilma this year. There’s an awful lot more that goes into cyclogenesis than just hot ocean water. But it means the potential is there. And in a year that has already shattered records left and right, I’m not betting against it.