Sam has continued to strengthen faster than predicted. It has reached hurricane strength and has developed a classic shape on the satellite as it tracks toward the Caribbean islands. It’s not moving as fast as many storms do in that part of the ocean, and is forecast to slow down over the warm Atlantic waters.
That means it will have lots of fuel to intensify, and the National Hurricane Center is predicting it will do so. A bit of Saharan air appears to be wrapping into the system now, but the forecast calls for Sam to become strong enough to expel the dry air and reach Category 4 strength by Sunday. Nobody would be surprised if it happened faster.
This is extremely late in the season for this strong a storm to develop so far out in the Atlantic. The ocean water between the Caribbean and Africa is near record warm, which no doubt is a contributing factor.
High pressure sprawled across the Atlantic is driving Sam to the west. The storm is more likely to move slower or faster depending on whether the high is weak or strong at the moment. Because the high is forecast to weaken, Sam is expected to slow to a brisk saunter over the next few days, which means it’s going to take an unusually long time to approach the Caribbean islands. The weaker high should also allow Sam to begin turning to the north.
Forecasts for slow-moving storms are always a bit iffier than systems that move at a regular rate. When the atmospheric push is relatively light, small unforecastable factors can affect the system’s movement. If the steering flow is strong, it tends to counteract the small issues that naturally occur. So we always have to keep the uncertainties in mind.
Having said that, by late in the weekend, a strong dip in the jet stream is forecast to be just offshore of the U.S. East Coast. This should push the steering high-pressure system to the east and open up a channel well east of the Bahamas for Sam to follow to the north.
It’s a fairly straightforward weather pattern, though the open questions remain, does Sam drift far enough north to be grabbed by the jet-stream dip? And does the dip plunge far enough south to grab Sam?
The computer forecast models mostly think the dip will scoop up the hurricane, but they disagree how close Sam will get to the islands before that happens. Everybody in the northeastern Caribbean islands needs to stay informed. A significant effect there can’t be ruled out.
Sam wouldn’t be approaching the islands until the middle of next week, if it does. For now, everybody just needs to stay informed.
If Sam takes the track to the north, Bermuda could be in the threat zone, and looking way down the road, an effect in New England and Atlantic Canada wouldn’t be impossible. Assuming Sam takes the open door to the north, of course.
Elsewhere in the Atlantic, the system that was Odette now only has a slight chance to become at least quasi-tropical before it gets absorbed into a large low-pressure area that also involves the remnants of Rose.
The next African system will emerge into the Atlantic late Sunday or Monday. Early indications are that it will be on a southern track like Sam, so it will have to be watched. It’s likely to develop into a tropical storm, based on the current forecasts.
Well offshore of the Carolinas, a non-tropical system has a short window of time to become tropical enough to become a depression or get a name. In any case, it will move away to the north.
The next two names are Teresa and Victor, in case one or both or the potential systems gets named. We’re fast approaching the end of the primary list of names for 2021. There are no “X”, “Y” or “Z” names in the list.
Effective this year, the World Meteorological Organization developed a backup list of somewhat funky names. If we need to use it, and it looks likely we will, we’ll start over with another “A.”