Weakening as expected on approach – but already a high-profile flood producer – Tropical Storm Henri made landfall at 12:15 p.m. EDT Sunday, August 22, near Westerly, Rhode Island, with a central pressure of 989 millibars. Henri had been downgraded from its category 1 hurricane status at 7 a.m. EDT Sunday as it traversed the cool waters north of the Gulf Stream en route to the U.S. coast.
Henri’s top sustained winds at landfall were 60 mph, and these were expected to decrease rapidly as Henri moves northwest toward western Massachusetts. Henri is predicted to slow to a crawl on Sunday night before turning sharply eastward toward Maine on Monday.
Oddly, Henri made landfall at virtually the same spot as Tropical Storm Elsa on July 9, and at the same time of day.
As Henri approached the coast, Weatherflow stations reported sustained winds of 40 mph gusting to 52 near Narragansett, RI, and 39 mph gusting to 49 at Block Island, MA. Just before landfall, Henri passed about 15 miles east of Montauk Point at the eastern end of Long Island, New York. Top winds at Montauk were 24 mph, with a peak gust of 45 mph. Well east of Henri’s center, Nantucket Island, MA, reported winds of 24 mph gusting to 33 mph.
Few additional locations are likely to experience sustained tropical-storm winds (39 mph) now that Henri is moving inland. Henri’s relatively slow motion for a New England tropical cyclone prevented the highest winds from moving too far inland before the storm decays, and it also reduced the additive factor that storm motion provides to peak winds.
Storm surge with Henri was modest, and its effects were limited by the fact that Henri’s onshore push peaked at most locations between the Sunday morning high tide and the Sunday afternoon low tide. As a result, highest water levels with Henri generally occurred during the Sunday morning high tide. Some peak surge values observed as of 3 p.m. EDT, together with peak storm tide (storm surge plus local astronomical tide, measured relative to mean low low water, or MLLW):
2.2’ at New London, CT (peak storm tide 4.5’);
2.1’ at Montauk Point, NY (peak storm tide 4.5’);
2.0’ at Newport, RI (peak storm tide 5.8’);
1.7’ at Woods Hole, MA (peak storm tide 3.7’).
Henri’s powerful rainfall punch
Heavy rains and flooding were by far the biggest threat Henri posed on Sunday. Dry air entering the storm will keep the heaviest rains focused toward the west side of Henri, mainly across western Connecticut and Massachusetts, southeast New York, and northern New Jersey.
As Henri churned well offshore on Saturday night, a nearly stationary corridor of showers and thunderstorms developed from Henri northwest across New Jersey and far southeast New York, producing massive rainfall and flash flooding in some highly populated areas. The CoCoRaHS volunteer observing network reported these 24-hour totals as of Sunday morning:
7.94” East Windsor Township NJ;
6.88” Plainsboro Township NJ;
6.69” Hopewell NJ;
6.16” Brooklyn NY.
The National Weather Service/New York office reported widespread mesonet totals on Saturday night of 4-6” in Brooklyn and 1-4” in Queens.
Some mesoscale forecast models correctly predicted the heavy rains across southern and central New Jersey but missed the narrow ribbon of rains that streamed across the New York City area on Saturday night. The feature was “PRE-like” in that it partially resembled a Predecessor Rain Event (PRE), a large zone of rain that can develop along pre-existing frontal zones hundreds of miles north of an incoming tropical cyclone.
New York’s Central Park recorded an impressive 4.45” of rain in a four-hour period up to midnight Saturday night. This included a one-hour total of 1.94” between 10 and 11 p.m. EDT that was reportedly the highest one-hour total on record at Central Park, apparently going back to 1943. This is a surprisingly low amount for a one-hour rainfall record in the relatively wet northeast U.S. Rainfall records can vary greatly across small areas: on August 13, 2014, Long Island MacArthur Airport (about 50 miles east of Manhattan) received 5.34” in one hour and 4.37” in the following hour.
Daily rainfall measurements began at Central Park in 1869, but one-hour precipitation readings were not widely collected at area sites until the 1940s, when the growth in aviation demanded more frequent rain and snow information.
Saturday night’s torrent caused widespread street and subway flooding across the New York area. It also led to disappointment for thousands at Central Park, as the We Love NYC Homecoming Concert was interrupted and cancelled because of lightning nearby. The concert was shut down in the middle of a Barry Manilow performance, literally seconds after Manilow sang the words “I just can’t smile…” (a moment that seemed painfully appropriate in this year of pile-on crises).
Henri the fifth U.S. landfalling storm of 2021
Henri’s landfall in Rhode Island makes it the fifth named storm to make landfall in the U.S. this year, coming after Fred (landfall on August 16 with 65 mph winds in Florida, killing five and causing over $200 million in damage); Elsa (landfall on July 7 with 65 mph winds in Florida, killing one and causing $775 million in damage); Danny (landfall in South Carolina on June 28 with 45 mph winds, no deaths or damages reported), and Claudette (landfall on June 19 in Louisiana, killing 14 and causing $350 million in damage).
Last year had a record 11 named storms make landfall in the contiguous U.S., beating the old record of nine set in 1916. The fifth U.S. landfall of 2020 (Isaias in North Carolina) occurred on August 4.
Over the 71-year period 1950-2020, the U.S. averaged three landfalling tropical storms (with one being a hurricane) per year, according to the website Tropical Storm Risk, so 2021 has already had more than an average season’s worth of landfalling storms. On average, about 70% of the Atlantic’s named storms occur after August 22; the average peak date of the season (September 10) is over two weeks away.
Climate change and Henri: An early look at links
There are some things we can note about climate change with respect to Henri long before there’s been a chance to carry out any potential attribution research.
A hurricane heading for New England: The preindustrial climate was fully capable of producing hurricanes in New England and New York. In fact, the current span of time since a landfalling hurricane has reached Long Island or New England—just over 30 years, since 1991’s Hurricane Bob—is the second longest in 170 years of recordkeeping. (Sandy in 2012 made landfall in New Jersey.) The fact that Henri failed to arrive as a hurricane will only keep the string going.
Henri’s subtropical genesis: Among tropical cyclones affecting New England, Henri is a clear anomaly in its formation and growth over the subtropics, near and north of 30°N. No hurricane on record has come ashore on Long Island or New England without having taken shape in the tropics, and few tropical storms or depressions. Warmer waters may have contributed to such behavior. Human-caused warming over the past few decades is strongly associated with higher sea surface temperatures. Most of Henri’s life prior to landfall was spent over waters that are about 0.5 degree C (0.9°F) warmer than average for the season. That long-term average itself is higher now than it was several decades ago. Warmer waters support stronger hurricanes and allow for development in more places and at more times.
Henri’s weird track: Henri’s northwestward motion over southern New England will be close to unprecedented for a tropical storm (see Figure 1.) And Henri will move across the region more slowly than almost any tropical storm on record. Henri’s behavior follows an observed trend towards slower-moving tropical cyclones over land in the U.S., which may have linkages to climate change.
Storm surge: Sea level has risen a few inches over the past century along the coast of southern New England, mainly as the result of human-produced warming together with related changes in ocean circulation. Sea level rise adds to the impact of the storm surge from any tropical or nontropical system, including Henri.
Intensified rainfall: Ample research has demonstrated that the most intense rainfall events, such as the epic downpours in New York and New Jersey on Saturday night ahead of Henri, are becoming more likely, chiefly as a result of warmer oceans evaporating more moisture for rainmaking systems to draw on.
In a nutshell, the landfall of a hurricane as a tropical storm in New England isn’t that exceptional in historical context, but Henri’s excessive rains are certainly aligned with what our human-altered climate is doing across the globe.
A rough historical analogue for Henri of 2021: Henri of 1985
Slow-moving tropical cyclones that affect New England are uncommon, since the jet stream is usually active that far north, bringing strong upper-level winds that typically move storms along at rapid forward speeds in excess of 20 mph. Curiously, one historical analogue storm for Henri of 2021 – a storm that moves relatively slowly towards a New England landfall – was an earlier incarnation of Henri, from September 1985.
Similar to this year’s Henri, the 1985 version of the storm got its start in subtropical waters well north of the Caribbean. Moving northward at about 10-15 mph after developing into a tropical depression, Henri became a tropical storm when it reached the warm waters of the Gulf Stream off the coast of North Carolina. After reaching a peak intensity of 60 mph along the northern boundary of the Gulf Stream, offshore from the North Carolina/Virginia border, Henri of 1985 quickly weakened over the cold waters to the north, hitting Long Island, New York, as a minimal tropical storm with 40 mph winds. There were no deaths or injuries from the storm, and little damage.
Henri of 2021 is a somewhat different beast. Ocean temperatures are much warmer than in 1985, so this year’s Henri had a lot more fuel to fire it up, and the human-warmed atmosphere carries more water vapor, allowing a storm like Henri to drop heavier rains. But just like Henri of 1985, Henri of 2021 moved northward at a relatively low speed over the cool waters north of the Gulf Stream during the final day of its approach to New England, and that induced considerable weakening.
Another key difference: Henri in 1985 was followed in less than three days by destructive Gloria, the most recent hurricane to make landfall on Long Island. This time, no tropical cyclones are expected across the Atlantic over the next several days. The 2 p.m. EDT Sunday tropical weather discussion from the National Hurricane Center gave 10 percent odds that a disturbance in the eastern Atlantic could develop into a tropical depression by Friday.
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