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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 3:43 PM GMT on February 07, 2013
A potentially historic Nor'easter is brewing for the Northeast U.S., where blizzard watches are up for much of eastern Massachusetts, Rhode Island, and Connecticut. The storm, dubbed "Nemo" by the Weather Channel, is expected to bring heavy snows of 1 - 2 feet, coastal wind gusts over hurricane force, and moderate to major coastal flooding. During the peak of the storm, Friday night into Saturday morning, snowfall rates of 2 - 3" per hour can be expected. These intense bursts of snow may be accompanied by lightning and thunder. The cites of Boston, Hartford, Providence, Portland, and Burlington are all likely to get more than a foot of snow, and two feet of snow will probably fall along a swath from the western suburbs of Boston to Southwest Maine. With the Nor'easter generating these heavy snows expected to bomb out with a central pressure of 972 - 976 mb, the rapid flow of air around this low pressure center will generate ferocious sustained winds near 50 mph at the coast, with wind gusts in excess of hurricane force--74 mph. The combination of heavy snow and high winds will make travel extremely dangerous or impossible, with near-zero visibility in white-out conditions. Total snowfall from the storm is likely to rank in the top ten for Boston since weather observations began at Logan Airport in 1936. According to NWS, here are the top snowstorms since 1936 for Logan Airport:
1. February 17-18, 2003 27.5"
2. February 6-7, 1978 27.1"
3. February 24-27, 1969 26.3"
4. March 31-April 1, 1997 25.4"
5. January 22-24, 1945 22.8"
6. January 22-23, 2005 22.5"
7. January 20-21, 1978 21.4"
8. March 3-5, 1960 19.8"
9. February 16-17, 1958 19.4"
10. February 8-10, 1994 18.7"
11. January 7-8, 1996 18.2"
11. December 20-22, 1975 18.2"
11. December 26-27, 2010 18.2"
Figure 1. Predicted wind speeds in knots at 7 am EST Saturday, February 9, 2013, from the 00Z February 7, 2013 run of the European (ECMWF) model. The model is predicting sustained winds of 50 knots (57.5 mph) will affect Cape Cod and Nantucket Island, Massachusetts. Multiply by 1.15 to convert knots to mph.
Serious coastal flooding expected in Massachusetts
The high winds from the storm will drive a damaging storm surge of 2 - 4' along the coast of Eastern Massachusetts Friday night and Saturday morning. Of particular concern is the flooding that will occur during the Saturday morning high tide cycle, as that is the time of the new moon, which will bring the highest tide of the month. The ocean's height in Boston varies naturally by about ten feet between low tide and high tide, so it matters greatly when the storm surge arrives, relative to the tidal cycle. Thus we speak of the "storm tide"--how how the water gets above the high tide mark, due to the combination of the storm surge and the tide. During Hurricane Sandy, on October 29, 2012, a potentially very damaging storm surge of 4.57' hit Boston, but arrived near low tide, so the water level during the peak surge did not rise above the normal high tide mark. As of noon EST on February 7, 2013, the latest storm surge forecast from the GFS model is calling for a storm tide of about 3.4' above high tide (MHHW, Mean Higher High Water) on Saturday morning, which would cause only minor flooding in Boston. This would be the 10th highest water level on record in Boston since tide gauge records began in 1921. According to former NHC storm surge expert Mike Lowry, who now works for TWC, the official top 5 storm tides at the Boston tide gauge, relative to MHHW, are:
1. 4.82' - February 7, 1978 (Blizzard of 1978)
2. 3.92' - January 2, 1987
3. 3.86' - October 30, 1991 (Perfect Storm)
4. 3.76' - January 28, 1979
5. 3.75' - December 12, 1992
More serious flooding is expected in Cape Cod Bay to the southeast of Boston, where the northeast winds from the storm will pile up a higher storm surge. A storm surge of 3 - 4' is predicted from Scituate to Sandwich Harbor Saturday morning. The surge will be accompanied by battering waves 20' feet high, and major flooding and coastal erosion is expected. Major coastal flooding is also expected on the east end of Nantucket Island.
Figure 2. Coastal flooding hazards during the high tide cycle on Saturday morning, February 9, 2013, as predicted at 12 pm EDT Thursday, February 7, 2013, by the NWS Boston.
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