Above: Waves crash over houses in Scituate, Mass., on Thursday, March 1, 2018. Image Credit: Scott Eisen/Getty Images.
States of emergency were declared on Saturday in Massachusetts, Virginia, and Maryland, after Winter Storm Riley brought hurricane-force wind gusts, a destructive storm surge, and heavy rain and snow to the Northeast and Mid-Atlantic. At least seven deaths have been blamed on the storm, and more than 2 million customers lost power. The National Guard was activated in Massachusetts and Pennsylvania to assist in the aftermath.
|Figure 1. GOES-16 satellite image of Winter Storm Riley, taken at 11:30 am EST Saturday, March 3. The huge storm covered most of the Northwest Atlantic, and was bringing near-record storm tides to Eastern Massachusetts. Image credit: NOAA.|
“Bomb” nor’easter generates hurricane-force wind gusts in 6 states
“Bombogenesis” occurs when the central pressure of a storm drops at least 24 millibars (mb) in 24 hours, and Friday’s “bomb” cyclone achieved that standard, with the central pressure falling to its lowest value of 974 mb at 7 am EST Saturday morning. Wind gusts in excess of 50 mph were recorded in 13 states, plus the District of Columbia, and six of those states had wind gusts of at least hurricane force (74 mph) on Friday and Saturday, according to NOAA:
BARNSTABLE 93 mph
EAST FALMOUTH 92
OAK BLUFFS 88
WOODS HOLE 88
MARSTONS MILLS 80
VINEYARD HAVEN 75
HAYANNIS AIRPORT 74
BRANDYWINE SHOAL NOS 74
MIDDLE ISLAND 78
LITTLE COMPTON 83
CHESAPEAKE LIGHT TOWER 79
DAHLGREN 3 NE 75
WINCHESTER 15 W 76
|Figure 2. Top wind gusts from Winter Storm Riley, courtesy of the NWS in Boston.|
A coastal flooding triple-whammy
Riley brought one of the most destructive coastal flooding events ever recorded from a nor'easter, thanks to a triple-whammy of unfortunate circumstances:
1) The storm was unusually powerful, with wind gusts in excess of hurricane force occurring along a large stretch of coast. This allowed the storm to pile up a storm surge that reached 4’ in Boston and Nantucket and 5’ at Chatham on Cape Cod. Fortunately, these peak storm surges occurred while the tide was going out on Friday afternoon, so Massachusetts did not see the highest water levels that it could have.
2) The storm hit during the full moon, when the highest tides of the month were occurring. Without the effect of the full moon, the top-ten storm tides observed in eastern Massachusetts would have been in the top twenty instead.
3) Riley was slow-moving, thanks to a blocking ridge of high pressure over Greenland. This brought near-record high water levels to the coast of New England during three consecutive tidal cycles, Friday morning through Saturday afternoon. Both Boston and Nantucket had top-ten highest storm tides on record during these three consecutive tidal cycles. That is an extremely rare occurrence, and one that I haven’t been able to find in the record books for any previous U.S. storm on record (detailed on-line data from U.S. tide gages at NOAA’s Tides and Currents website only go back a few decades, though.)
The highest storm tide observed at a major tide gaging station during Riley was 4.4’ above the high tide mark (Mean Higher High Water, or MHHW) at Boston at 11:12 am EST Friday, during the morning high tide cycle. This was the third highest water level ever recorded in Boston, and was close to a 1-in-100-year event. According to NOAA, a 1-in-100-year storm tide with a 1% chance of occurring in a given year in Boston is a water level of 4.59’ above Mean Higher High Water. Since records began in 1921, the only higher storm tides in Boston were 4.88’ above MHHW on January 4, 2018 in Winter Storm Grayson, and 4.82’ above MHHW on February 7, 1978, during the infamous Blizzard of ’78.
Here are storm tide readings from some selected tide gages during the three high tide cycles that occurred during Riley (see NOAA’s Quicklook page for a nice summary):
Portland, ME: 3.21’ (10th highest on record), 2.48’, 2.96’
Nantucket, MA: 3.05’ (7th highest on record), 3.13’ (6th highest), 3.21’ (5th highest)
Boston, MA: 4.4' (3rd highest on record), 3.6' (10th highest), 3.67' (8th highest)
Montauk, NY (east end of Long Island): 2.67’, 2.17’, 2.57’
King’s Point, NY (west end of Long Island Sound): 3.12’, 2.1’, 3.0’
New York City, NY: 2.15’, 1.2’, 2.23’
Snapped this picture an hour before high tide. The sign says it all. Sure makes you think..... pic.twitter.com/xy6Jl13GLM— Matt Beaton (@MattBeatonEEA) March 2, 2018
Riley brought heavy snows along a swath from Southeast Michigan to Western Massachusetts, with the heaviest snows falling in Upstate New York. Here are the heaviest snow amount by state from the storm, according to NOAA:
39.3”: Cobleskill, New York
23.6”: Coolbaugh, Pennsylvania
16.5”: Branchville, New Jersey
14”: Woodford, Vermont
12”: Plainfield, Massachusetts
7.4”: Wixom, Michigan
6”: Sharon, Connecticut
1.1”: Foster, Rhode Island
|Figure 3. Predicted rate of precipitation (in colors) and lines of constant pressure in millibars (black lines) for 8 pm EDT Wednesday, March 7, 2018, made by the 12Z Saturday run of the GFS model. A moderate-strength nor’easter with a central pressure of 991 mb was predicted to be south of Long Island, New York. The model predicted snow over New York City and rain over Boston for this snapshot in time. Image credit: tropicaltidbits.com.|
Another nor’easter coming on Wednesday
Our top computer forecasting models, the GFS and European models, have been predicting for several cycles now that another nor’easter will bring strong winds, heavy snow, and heavy rain to the Northeast U.S. on Wednesday, March 7. This storm is currently forecast to be much weaker than Riley, but it is too early to be confident of this. Since the storm will not be hitting during the full moon, though, coastal flooding will be considerably less than was observed for Riley.