Weather

H Henri: Upgraded to hurricane, forecast track moved slightly eastward

IMPORTANT: This post is out of date and has been superseded; see motifri.com/wx-henri-2021-08-21-2300edt

As of 11am EDT Sat, Aug 21, 2021 in RI:
• A Storm Surge Warning and Hurricane Warning are in effect for Newport and Washington Counties including Block Island.
• A Storm Surge Warning and Tropical Storm Warning are in effect for eastern Kent County.
• A Tropical Storm Warning is in effect for Providence and western Kent Counties.

Changes from 5am EDT:
A Hurricane Watch and Tropical Storm warning have been upgraded to a Hurricane Warning for Newport and Washington Counties including Block Island.
A new Tropical Storm Warning has been issued for Providence County.
A Hurricane Watch has been canceled for Bristol and Kent Counties.

The latest guidance as of 11am EDT Sat, Aug 21, upgrades Henri to official hurricane status with maximum sustained winds of 75MPH, hurricane force winds extending 60 miles and tropical storm force winds 125 miles from the center, an increase in size. Additional strengthening is likely overnight, although some weakening from peak strength is expected before landfall at or near hurricane strength Sunday morning.

Computer models moved the forecast track back slightly eastward, with RI now on the eastern edge of possible landfall, but the exact point of landfall is of lesser concern as effects will be felt well to both the west and east of the center so focus on the precise track can be misleading.

Tropical Storm Henri: Probability of tropical storm force winds for five-day period beginning Sat Aug 21, 2021, 8am EDT.

Providence has 84% probability of experiencing tropical storm force winds (39MPH) and 11% probability of hurricane force winds (74MPH), capable of significant damage.

Based upon prior guidance from the 5am forecast cycle that has not yet been updated, RI remains in the “slight” 10% risk band for flash flooding due to excessive rainfall. RI is forecast to receive 1-2 inches of rain, considerably less than the 6-10 inches in central Long Island and 4-6 inches along the CT coast. Storm surge of 1-3 feet is possible on the RI coast and within Narragansett Bay.

Rain is likely to begin by Sun, Aug 22, 1am and end by 11pm with peak sustained winds exceeding 20MPH from 11am to 7pm.

Tropical Storm Henri: Probability of excessive rainfall and flash flooding for three-day period beginning Sat Aug 21, 2021, 8am EDT.
Tropical Storm Henri: Probability of total rainfall for three-day period beginning Sat Aug 21, 2021, 8am EDT.

The worst effects are likely to stay west of RI, but there is little difference in practical effect whether the storm is slightly above or below the arbitrary threshold of 74MPH that would classify it officially as a hurricane, and the potential for harm from heavy rain, high winds, and storm surge, as well as life-theatening surf and rip currents, should be taken seriously. All of southern New England can expect what amount to hurricane conditions, regardless of whether they meet the technical criteria.

All tropical weather systems should be regarded as volatile and unpredictable to some extent, so it is a mistake to focus on the exact forecast point of landfall as that may change significantly before it occurs. While this storm is extremely unlikely to “go out to sea” harmlessly, it would be no surprise to see the forecast track move back and forth closer to and farther away from RI, and it would be prudent to prepare for any possibility, charging cellular telephones and making sure flashlights and other equipment is powered and ready. Loss of electrical power mains for as long as several days should be part of planning.

[The RI Emergency Management Agency uses the CodeRED system to allow the public to sign up for direct community notifications: public.coderedweb.com/CNE/en-US/BF1E5F52D694 ]

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