Whenever the organization tasked with identifying and tracking hurricanes raises a flag before the hurricane season begins, it does raise an eyebrow. The National Hurricane Center says this disturbance in the Bahamas is worth watching, but is not presenting an immediate threat. So many of us in Houston are still picking up the pieces of our lives after the flooding rains from Tropical Storm Harvey (downgraded from a Cat 4 hurricane) so news of this is not welcome. While June 1st marks the start of the hurricane season -- which lasts until November 30th -- we've actually seen about 88 tropical systems form outside of the defined hurricane season since 1851. (I say, "about" because in the pre-satellite era, starting around 1960, identification of tropical systems were done by ship reports which were unreliable at times because you'd have to have a boat in the vicinity of a storm to, "see it." We did not have weather satellites -- or aircraft for that matter -- zipping around taking pictures of the Earth 24/7.)
Out-of-season systems are actually quite common. As recently as last year, Tropical Storm Arlene (in the open Atlantic) formed in mid-April. It happens more commonly than you may think. It works both ways: some seasons seem to never end. In the 2005 season, our last system dissipated in early January of the following year: 2006!
Now, some have pointed out that the NHC has, "clearly" said this system has a, "0% chance of forming." Two things to note: First, they mean a, "zero percent chance in the next 48 hours." It still could develop after that time period as many have. Second, this is their weather forecast (which does not mean it's written in stone -- it's just a highly educated opinion.) I've also seen, "0% chances" become named systems unexpectedly. An example of this type of uncertainty? HARVEY! On August 19, 2017 it was listed as, "dissipated" by the NHC while sitting over the open Caribbean sea. That means it lost its tropical characteristics and classification as a cyclone. It was dead in the water like a jet ski that ran out of gas. Here was the text advisory [link]:
NEXT HARVEY ADVISORY -------------This is the last public advisory issued by the National Hurricane Center on this system unless regeneration occurs or if tropical cyclone watches or warnings are required for land areas. Additional information on this system can be found in High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and available on the Web at http://www.opc.ncep.noaa.gov/shtml/NFDHSFAT1.shtml.
There was no forecast offered by NHC beyond that for six days.... until August 24th. Because it had already been named, no percent chance for regeneration was offered on 8/19. You could call it a less than zero percent chance of forming since they weren't offering a percent. (I know math nerds: you can't have a less than 0% chance... but go with me: I'm bringing the jargon down the Earth.) Many forecasters simply wrote it off and focused instead on other disturbances in the Atlantic farther east. Of course, a little more than a week later, Harvey would become a Category 4 hurricane and make landfall north of Corpus Christi and then flood Houston with a historic deluge.
The moral of this blog is that the tropics are fickle and absolutely unpredictable. Things change often and they change fast. PREPARE NOW. If you don't prepare after last year, you probably never will so I'm probably preaching to the choir. But seriously, it's best as we are constantly reminded, to never completely let your guard down at what may seem to be downplayed outlooks. Would you go to sleep with a mosquito clinging to the wall in your room, trusting it's not going to bite? -Meteorologist Brooks Garner