September is prime time for the Atlantic Hurricane Season, but it hasn’t lived up to the reputation this year. There have been no hurricanes anywhere in the Atlantic since Hermine dissipated on September 2nd. According to Philip Klotzbach, it’s only the 10th time in the past 116 years that there hasn’t been a hurricane from September 3rd through 27th, and the first time since 1994. A number of factors like wind shear and dry air have prevented strong development. But that streak may come to an end this week.
The system we’re keeping tabs on is approaching the Lesser Antilles and is slated to become ‘Matthew’ in short order. There’s good news and bad news about this storm. The good news is that we have a very good idea of what it’s going to do over the next 4-5 days. The bad news is there’s a high stakes game of ‘what if’ after that point and little clarity about the longer range track and intensity. No doubt you’re going to see people pass around/post single model runs showing worst case scenarios and direct hits on the U.S. coast. But we in weather know it’s shades of gray and not black and white – and that it’s poor form to cherry pick and hype things up. Especially when we’re so far out (7+ days) from a U.S. impact and there is little to no skill in predicting a tropical storm that far out. So let’s start with the high confidence stuff, and move on from there!
ECMWF EPS (ensemble prediction system) tracks for future ‘Matthew.’ A very tight range of tracks for the next several days, indicated by the red zone. After that, all bets are off. Source: UAlbany Tropical Cyclone Guidance
For starters, a movement to the west is the expected path. This brings the storm through the Windward and Leeward Islands, and then into the open waters of the Caribbean late this week and into the weekend. By Saturday/Sunday, it should be taking up residence south of Hispaniola. If you’re a tropical system this time of year, this is where you want to live. The water is still very warm (about 85-88F) and it’s often a comfortable spot to avoid wind shear (caveat: El Nino years). In other words, the environment is very favorable. Not only is that water warm, but the heat potential is extremely high with the warm waters extending deep below the surface. That’s lots of energy for a storm to explode, provided wind shear relaxes. The real ‘hot spot’ is around and to the west of Jamaica, which is indeed a possible landing spot for Matthew. If it can tap these waters, it could strengthen rapidly and become a very powerful hurricane. It’s the type of situation where guidance can sometimes be thrown out the window, because a storm can go from decent to a monster in a short amount of time and this rapid change is not often captured in the models.
That’s a nice lead-in for a talk about intensity. While models are not in good agreement about the track, there is a common theme about power. Nearly all of the members of ECMWF and GFS ensembles produce a healthy hurricane. That’s a very strong signal for development. We haven’t had any real powerhouse storms near land this year (Gaston is the only Category 3 so far in the Atlantic). So this alone warrants attention. A storm in the Caribbean doesn’t really have anywhere to go without hitting land, which means a destructive impact is looking more likely irregardless of where it tracks.
This fun plot, which looks like a petri dish full of lord knows what, helps to illustrate the low confidence once the storm starts to head north. It’s a look at all 51 members of the ECMWF model. These members are all on the same team, so to speak. But each has their initial conditions tweaked a bit. If little tweaks don’t change the outcome, you typically have a high confidence forecast. If they diverge, it means that you have a sensitive situation with a lot of possibilities on the table. I think this image speaks for itself. You have potential tracks anywhere from Central America to east of the Bahamas. But also note that many of them are quite strong (low pressure).
Compare this to the GEFS, and the picture gets more muddled. The GEFS has been very consistent and in extremely good agreement about where Matthew will go, but the problem is that doesn’t mean it’s right. It may mean that it’s just very, very wrong. We saw this with Hermine, as almost all the GEFS members took the storm east of Florida for a time before coming around to the Gulf track. Just because they all agree doesn’t mean we can lock it in. So we have two dramatically different camps. What to do?
At this point in time, it just is what it is. As I mentioned above, there’s no skill in taking a system that’s barely even formed yet and projecting it out 7-10 days. It’s not like predicting cold/warm wet/dry trends, which has become fairly routine in the 1-2 week range or longer. There are delicate steering currents that will dictate where Matthew goes. We know that it’s going to pose a threat in the Caribbean; that Hispaniola, Jamaica, and Cuba should be watching it very closely as they have the highest threat right now. There is still too much uncertainty to say whether it will end up toward the Gulf, into Florida, or into the Bahamas next week. The other X-Factor is how much land interaction occurs. A path across the mountainous parts of Cuba or Haiti/Dominican Republic can shred a tropical system, while shooting the gap between them could allow it to retain intensity. Lots of questions remain, though if I had to place a bet I’d say the GFS will start caving to the Euro guidance and trend more west toward Cuba and Florida over the next couple days.
It’s a good time to be watchful and make sure you have your hurricane preparedness plan in order, as is always the case here in peak hurricane season. There’s no reason to change plans or start shuttering up the houses this far out. So keep up to date and I would expect the ultimate path to become much more clear by this weekend. October hurricanes are rare in New England because of the cooling waters, but we’re near all-time record warm water for this time of the season. Certainly a tropical system could sustain itself, especially if it’s moving quickly. We’re in ‘watching mode’ for now and naturally we’ll let you know if we need to make the jump to ‘alert’ status in the days ahead!
Water temperatures are running very warm for this time of year all across the western Atlantic. Temps near 70F extend all the way to Long Island. Source: Weatherbell