Henri was on track last weekend to be the first landfalling hurricane in New England in three decades. But just before touching land in Rhode Island on Aug. 22, it lost steam and was downgraded to a tropical storm.
Even in its weakened state, with winds of about 60 mph, Henri was still pretty significant and drenched places that rarely see such tropical weather, like parts of Connecticut, New York, New Jersey and Pennsylvania.
Philip Klotzbach, a research scientist at Colorado State University’s Department of Atmospheric Science, said it is not super common for New England to experience tropical cyclones, but it does happen.
Probably the biggest storm on record to hit that part of the country was the 1938 hurricane referred to as the Long Island Express.
“That was a really big, really nasty, super-fast moving storm that was a Category 3 hurricane,” Klotzbach said.
And Bob in 1991 — Henri’s predecessor — was a Category 2 storm with winds of about 105 mph when it came ashore. The storm was responsible for 17 deaths and $1.5 billion in damage, according to a report from the Associated Press.
There are several factors that usually prevent a tropical cyclone from making it as far north as New England. Klotzbach said it requires a unique steering.
Hurricanes need really warm water of at least 80 degrees to thrive, he said. The waters right off the coast of New England are usually fairly cool and in the low 70s this time of year. These temperatures are not enough to sustain the storm for the long term.
That is why Henri weakened a decent amount when it encountered the cooler New England waters.
“Typically when you get really powerful hurricanes up into New England, the reason they’re so powerful is because they’re moving very quickly,” Klotzbach said. “So even though the waters are getting cooler, if the storm is moving 30 to 40 miles an hour, it’s just not over that cold water for very long until it’s up on shore.”
Klotzbach said it is a bit of a stretch to tie Henri to climate change. He said folks could argue that the waters are warmer than normal, but some of that is because there was a pronounced atmospheric circulation that cooled the tropical Atlantic and warmed the mid-latitude Atlantic last winter.
“And it was probably somewhat of a climate change component to that warming, Klotzbach said. “But trying to figure out if the water is 3 degrees warmer, what percentage of that was climate change versus natural is hard to do.”
The fact that New England's waters are currently a few degrees warmer than normal could be what helped keep Henri together a little longer.
There hasn’t been much evidence of increasing high pressure over New Brunswick and Nova Scotia, and that would be needed to actually get the storms to track up into southern New England, Klotzbach said.
Steering is another big component.
Dr. Cary Mock, a climatologist and geography professor at the University of South Carolina, said there has to be the right set of weather patterns at the right time to steer tropical cyclones toward New England.
And since that happens at random, Mock said there isn’t a clear trend to prove that the region is getting more or fewer storms.
Henri was a weird storm from the beginning, Mock said. It started in the western Atlantic, and the steering currents caused confusion for some scientists.
When the different high- and low-pressure systems — which dictate the winds — change intensity just a little bit, they can alter the track of the storm slightly. And some meteorologists ultimately predicted Henri would be much stronger than it turned out to be.
As of the morning of Aug. 24, remnants of the storm were forecast to produce about an inch of rain across portions of New Hampshire, Massachusetts and Maine. Maximum sustained winds were around 25 mph.