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TS Henri: Centered over Block Island, heading for mainland

IMPORTANT: This post is out of date and has been superseded; see motifri.com/wx-henri-2021-08-22-1700edt

UPDATE: As of 2pm EDT, Tropical Storm Warnings have been dropped for all of RI except Block Island, and maximum sustained winds have decreased to 50MPH as TS Henri loses strength over land.

As of 11am EDT Sun, Aug 22, 2021 in RI:
• A Storm Surge Warning and Tropical Storm Warning are in effect for eastern Kent, Newport, and Washington Counties including Block Island.
• A Tropical Storm Warning is in effect for Providence and western Kent Counties.

Tropical Storm Henri is centered over Block Island and is on a forecast track northwestward for a direct hit on the RI mainland, as of the guidance at 11am EDT, Sun, Aug 22, with the most likely path making landfall early afternoon in the area of Charlestown. Maximum sustained winds are 70MPH, just short of hurricane force: tropical storm force winds extend 125 miles from the center. Hurricane warnings have been lowered to tropical storm warnings in southern RI due to the slight weakening of the system.

NWS radar snapshot, composite reflectivity (CREF) from Boston (WSR-88D). TS Henri is centered over Block Island. The shaded region near New London, CT, is a Flash Flood Warning.

Rain has begun and will likely end by tonight 2am with peak sustained winds exceeding 20MPH until 8pm. The situation is favorable for the formation of tornadoes. A second period of rain is possible Mon 10am to Tue 2am, most likely 5pm to 10pm, but winds less than 15MPH.

Tropical Storm Henri: Probability of tropical storm force winds for five-day period beginning Sun, Aug 22, 2021, 8am EDT.

Although “probability cone” charts are liable to be misunderstood because they focus on the center of the storm and thereby ignore the field of wind that can extend across hundreds of miles on either side of that track, in this case the direct aim toward RI is striking and illustrative.

Tropical Storm Henri: Probability “cone” of track of storm center for five-day period beginning Sun, Aug 22, 2021, 11am EDT.

Most of RI except the extreme southwest remains in the “slight” 10% risk band for flash flooding due to excessive rainfall. RI is forecast to receive 2-4 inches of rain, considerably less than the 6-10 inches in central Long Island and 4-6 inches along the CT coast, but this soon could be revised upward. Storm surge of 3-5 feet is possible on the RI coast and within Narragansett Bay.

Tropical Storm Henri: Probability of excessive rainfall and flash flooding for three-day period beginning Sun, Aug 22, 2021, 8am EDT.
Tropical Storm Henri: Probability of total rainfall for three-day period beginning Sun, Aug 22, 2021, 2am EDT.

TS Henri is just short of hurricane strength with maximum sustained winds at 70MPH, 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 ]




H Henri: Most likely track still a direct hit on RI

IMPORTANT: This post is out of date and has been superseded; see motifri.com/wx-henri-2021-08-22-1100edt

As of 5am EDT Sun, Aug 22, 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.

Hurricane Henri remains on a forecast track for a direct hit on RI, as of the guidance at 5am EDT, Sun, Aug 22, with the most likely path coming straight up Narragansett Bay, making landfall late morning or early afternoon as a Category 1 hurricane on the Saffir-Simpson scale. Maximum sustained winds are 75MPH: hurricane force winds extend 35 miles and tropical storm force winds 125 miles from the center.

Rain is likely to begin by Sun, Aug 22, 6am and end by Mon 2am with peak sustained winds exceeding 30MPH and gusts exceeding 50MPH from 4pm to 11pm. At Providence, sustained winds to 55MPH and gusts to 70MPH are possible. The situation is favorable for the formation of tornadoes. A second period of rain is possible Mon 10am to Tue 2am, but only about 30% likely and winds less than 15MPH.

NWS radar snapshot, composite reflectivity (CREF) from Boston (WSR-88D).

Because low pressure centers such as storms have counter-clockwise airflow (in the Northern Hemisphere), regions to the east of the track receive higher velocity wind with the forward motion of the storm added while regions to the west of the track receive higher rainfall.

Providence has 99% probability of experiencing tropical storm force winds (39MPH) and 10% probability of hurricane force winds (74MPH), capable of significant damage.

Tropical Storm Henri: Probability of tropical storm force winds for five-day period beginning Sun, Aug 22, 2021, 2am EDT.

Although “probability cone” charts are liable to be misunderstood because they focus on the center of the storm and thereby ignore the field of wind that can extend across hundreds of miles on either side of that track, in this case the direct aim toward RI is striking and illustrative.

Tropical Storm Henri: Probability “cone” of track of storm center for five-day period beginning Sun, Aug 22, 2021, 5am EDT.

Most of RI except the extreme southwest remains in the “slight” 10% risk band for flash flooding due to excessive rainfall. RI is forecast to receive 2-4 inches of rain, considerably less than the 6-10 inches in central Long Island and 4-6 inches along the CT coast, but this soon could be revised upward. Storm surge of 3-5 feet is possible on the RI coast and within Narragansett Bay.

Tropical Storm Henri: Probability of excessive rainfall and flash flooding for three-day period beginning Sun, Aug 22, 2021, 8am EDT.
Tropical Storm Henri: Probability of total rainfall for three-day period beginning Sun, Aug 22, 2021, 2am EDT.

H Henri remains at hurricane strength with maximum sustained winds at 75MPH, 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 ]




H Henri: Most likely track a direct hit on RI

IMPORTANT: This post is out of date and has been superseded; see motifri.com/wx-henri-2021-08-22-0500edt

As of 11pm 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.

Hurricane Henri is on a forecast track for a direct hit on RI, as of the guidance at 11pm EDT, Sat, Aug 21, with the most likely path coming straight up Narragansett Bay, making landfall as a Category 1 hurricane on the Saffir-Simpson scale. Maximum sustained winds are 75MPH: hurricane force winds extend 35 miles and tropical storm force winds 150 miles from the center.

Rain is likely to begin by Sun, Aug 22, 5am and end by Mon 2am with peak sustained winds exceeding 30MPH and gusts exceeding 50MPH from 4pm to 11pm. A second period of rain is possible Mon 10am to Tue 2am, but only about 30% likely and winds less than 15MPH.

Because low pressure centers such as storms have counter-clockwise airflow (in the Northern Hemisphere), regions to the east of the track receive higher velocity wind with the forward motion of the storm added while regions to the west of the track receive higher rainfall.

Providence has 98% probability of experiencing tropical storm force winds (39MPH) and 19% probability of hurricane force winds (74MPH), capable of significant damage.

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

Although “probability cone” charts are liable to be misunderstood because they focus on the center of the storm and thereby ignore the field of wind that can extend across hundreds of miles on either side of that track, in this case the direct aim toward RI is striking and illustrative.

Tropical Storm Henri: Probability “cone” of track of storm center for five-day period beginning Sun Aug 22, 2021, 2am EDT.

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, but this soon could be revised upward. Storm surge of 3-5 feet is possible on the RI coast and within Narragansett Bay.

Tropical Storm Henri: Probability of excessive rainfall and flash flooding for three-day period beginning Sun Aug 22, 2021, 8am EDT.
Tropical Storm Henri: Probability of total rainfall for three-day period beginning Sat Aug 21, 2021, 8pm EDT.

H Henri remains at hurricane strength with maximum sustained winds at 75MPH, 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 ]




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 ]




TS Henri: Forecast track moved westward, reducing risk to RI

IMPORTANT: This post is out of date and has been superseded; see motifri.com/wx-henri-2021-08-21-1100edt

As of 5am EDT Sat, Aug 21, 2021 in RI:
• A Storm Surge Warning, Tropical Storm Warning, and Hurricane Watch are in effect for Bristol, eastern Kent, Newport, and Washington Counties, including Block Island.
• A Tropical Storm Warning and Hurricane Watch are in effect for western Kent County.

The latest guidance as of 5am EDT Sat, Aug 21, moves the forecast track of Tropical Storm Henri westward to make landfall over Long Island and continue into Connecticut, reducing the effects in Rhode Island, which is now moved into the “slight” 10% risk band for flash flooding due to excessive rainfall.

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 tropical storm force winds for five-day period beginning Sat Aug 21, 2021, 2am EDT.
Tropical Storm Henri: Probability of excessive rainfall and flash flooding for three-day period beginning Sat Aug 21, 2021, 8am EDT.

Providence still has a 75% probability of experiencing tropical storm force winds (39MPH) and a 7% probability of hurricane force winds (74MPH), capable of significant damage. 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.

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

Although RI seems likely to escape the worst effects, TS Henri is expected to strengthen over the next 12-18 hours before making landfall at or near hurricane force. There is little difference in practical effect whether the storm crosses the essentially 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 eastward toward RI and it would be prudent to prepare for that 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.




How I Became the Motif Weatherman

Weather is an endlessly fascinating topic: It affects everybody and can literally be a matter of life and death.

Forecasting seems to many some kind of black art, but the basic principles are fairly simple: Collect a lot of observations, plug them into a set of theoretical models, and turn the crank repeatedly to advance the scenario in steps of a few minutes at a time. Eventually this produces predictions 12, 24, 48, 72, or however many hours in advance are desired.

In the modern era, this is all done by the National Weather Service (NWS), a federal government agency, operating with extreme transparency and posting almost all of their data publicly, in real-time. NWS publishes narrative summaries aimed at the general public, but they also publish a lot of fairly technical discussions about the judgment calls they make, such as which models best predict particular weather conditions, aspects of uncertainty and so on.

Historical false-color satellite image of a blizzard approaching Providence, Jan 27, 2015, that would dump 18-24 inches of snow with wind gusts exceeding 50MPH and sub-zero wind chill.
Historical false-color satellite image of a blizzard approaching Providence, Jan 27, 2015, that would dump 18-24 inches of snow with wind gusts exceeding 50MPH and sub-zero wind chill.

Although there are private weather forecasting agencies, none have anywhere close to the resources of NWS and therefore all rely on observations collected by NWS and on computer processing of models by NWS. Everyone is working from the same baseline data, and NWS is very good at what they do. A few decades ago, if someone wanted to go into the private weather forecasting business, the first thing they needed was a dedicated feed of NWS data that was intended to be continuously printed by a teletypewriter, but now all of that information and more is freely available on the internet from weather.gov and related sites. When NWS started putting data on the internet in the 1990s, it was mostly a minimally parsed dump of that old teletypewriter feed, and it was not very popular: I wrote a script to poll the NWS server every few minutes to see if any severe weather alerts had been posted, and to my astonishment their published logs showed that I was the 20th heaviest user in the world of that data feed. Within the last 15 years or so, it became realistically practical to dive into raw NWS data and compile what amounts to one’s own forecast.

Why would anyone want to do this? Typical media weather forecasts are very dumbed down, masking complexity that while inherent in the science is a challenge to convey. Does the ordinary consumer of a weather forecast want to be presented with charts and graphs showing probability distributions? There is a perceived risk that the public will lose confidence in a forecast if it is presented with too emphatic an admission of uncertainty, and this discourages the preservation of nuance.

Severe weather can involve snowstorms and hurricanes that most people understand are difficult to predict, but fairly ordinary weather presents hard-to-summarize problems, too. The forecast may say there is a chance of rain, but at what times of day is it likely to start and end? Is the probability distribution actually multimodal, where the most likely scenarios are a lot of rain or no rain at all?

A few years ago, I began for my own purposes compiling weather forecasts from NWS data. My main goal was to cut through the oversimplification of typical media weather forecasts, trying to understand the subtleties and uncertainties being discarded in the presentation. This proved useful, and I began developing ways to summarize the results over social media while preserving both narrative clarity and nuance. These became popular among my friends and followers.

Among my responsibilities at Motif is distribution manager: I co-ordinate the process of physically moving tens of thousands of copies of the newsprint magazine to a few thousand delivery points throughout Rhode Island and nearby Massachusetts. We depend upon a fleet of drivers to do this, and we work to a rigid schedule because of constraints from our printing contractor.

The turning point where my interest in weather and my role at Motif crossed paths was a year ago in March, when I realized a snowstorm was going to hit during distribution. In the early morning hours of Saturday, Mar 11, 2017, I sent e-mail to the core staff:

I don’t want to alarm anyone and it’s too early to predict with good reliability, but right now the most likely scenario for the weather is a major snowstorm from about 11pm Mon to 4am Wed… as a practical matter near-blizzard conditions are expected, especially at the peak of the storm 9am – 5pm Tue with wind gusts as high as 40MPH… the amount of liquid associated with this storm will have the potential to drop as much as 18 inches of snow on somebody.

Motif editor Emily Olson, then 8 ½ months pregnant, jokingly replied, “So my labor starts Tuesday afternoon. Got it.” (It didn’t.) The real problem was that, three days in advance of a near-blizzard, the broader news media were not even talking about it, so public awareness was consequently very low. Even our printing contractor was about to be caught by surprise. While weather forecasting seems an odd fit for a magazine that publishes twice per month, it made sense to disseminate the information I was already developing for internal purposes, so we posted it on social media. It proved a big hit.

I learned a lesson years earlier in what came to be known as the “December Debacle,” when allowing schools to open and then conduct early dismissal threw the state into chaos, with parents scrambling to leave work in time to meet their children and the students thrust out on buses at the peak of the storm, trapping everybody in traffic for many hours. As I wrote about 7:30pm on Thursday, Dec 13, 2007, while snow was still falling:

I knew from the weather forecast that things would be bad in Providence, but I honestly did not expect things to get as bad as they did. I have not seen snow-caused road conditions this bad since the legendary Great Blizzard of 1978.… the key mistake in 1978, as everyone realized in hindsight, was allowing schools and businesses to open normally, in defiance of the forecast… Today, we have much better technology to cope with these kinds of situations, but we don’t use it properly. Aside from the fact that weather forecasting itself is far more accurate further in advance [than in 1978], e-mail and cell phones make it possible to disseminate information very quickly in order to effect cancellation notices.

I had an evening event scheduled on the day of the storm, and I began watching the forecast a day and a half earlier, sending out e-mail updates and announcing more than 24 hours in advance that the event would be postponed if there was no change in the forecast. By the morning, about two hours before snow began, I officially postponed my event. As I wrote at the time:

What I did was not some sort of brilliant prophecy, but rather simply trusting the accuracy of the forecast. I had a lot of detailed information at my disposal, with the National Weather Service data showing that the snow was likely to start no earlier than 9am and no later than 1pm, detailed predictive information beyond the technology of 1978…. In the end, this snowstorm should be a learning experience. We need to use the improved technology of weather forecasting to make decisions about closing schools and businesses sufficiently far in advance to do any good, and we need to use the improved technology of communications to disseminate those decisions quickly and reliably.

The lesson I learned, personally, was that people often don’t believe weather forecasts: The “December Debacle” occurred because an excellent, high-quality forecast that accurately predicted the weather almost exactly correctly and sufficiently far in advance was simply ignored by schools and businesses as well as by individuals. Clearly, they had been conditioned not to trust weather forecasts, but why?

My conclusion is that the hiding of uncertainty and complexity diminishes trust in the forecast. If the scientific model predicts a 60% chance of rain, so the forecast is dumbed-down to “rain” but there is no actual rain, then people see this as a wrong forecast; in truth, the forecast should have explained that there was a 40% chance of no rain. It may be frustrating for the public to be told it is almost a toss-up whether there will be rain, but that’s what it is.

Snow accumulation is a noteworthy case because everyone wants to know how much we might get. In connection with a blizzard warning on Jan 4, 2018, I posted: “The median accumulation forecast for Providence is 10 in, with probabilities near 100% for at least 0.1 in, 98% for 1 in, 97% for 2 in, 93% for 4 in, 86% for 6 in, 75% for 8 in, 37% for 12 in, and near 0% for 18 in.” In my opinion, it is a disservice to dumb this down to the typical “8-12 inches.”

Regarding a weather event on Feb 7, 2018, I explicitly pointed out that while snow was likely we could get all rain: “The median accumulation forecast for Providence is 1 in, with probabilities 71% for at least 0.1 in, 55% for 1 in, 40% for 2 in, 7% for 4 in, and near 0% for 6 in. Note that this implies a 29% chance of no snow at all.” I described the most likely scenario, saying that precipitation “…is likely to begin after 9am as snow, change to sleet and freezing rain starting around 12pm, and complete a change to rain by 3pm… Precipitation may turn back to snow briefly before ending around 1am…” The typical presentation would dumb that down to “wintry mix.”

Such detailed narratives with actual numbers and times, in my opinion, enhance the credibility of the forecast by communicating uncertainty in a useful way. Removing complexity and nuance by dumbing down forecasts fools people into disbelieving weather forecasts that were highly accurate before being oversimplified for typical media presentation.