Northeast to be Hit by Potent Storm NEMO

I guess, the folks in the Northeast will not need to find Nemo.  It seems Nemo is finding them:

Dr. Jeff Masters’ WunderBlog

Historic Nor’easter poised to slam Boston and the Northeast U.S.
Posted by: Dr. Jeff Masters, 3:43 PM GMT on February 07, 2013 +18

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 the 1950s. Here is the current top-10 list 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 22-23, 2005 22.5″
6. January 20-21, 1978 21.4″
7. March 3-5, 1960 19.8″
8. February 16-17, 1958 19.4″
9. February 8-10, 1994 18.7″
10. January 7-8, 1996 18.2″
10. December 20-22, 1975 18.2″
10. 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.

I’ll have an update on the storm Friday morning.

Jeff Masters


Latest on TS/Hurricane Isaac

Isaac approaching hurricane strength
Posted by: Angela Fritz, 9:14 PM GMT on August 27, 2012 +26

Isaac is walking the line of hurricane status this afternoon after a hurricane hunter mission investigated the storm and found winds of 80+ mph with the SFMR instrument, which looks down at the surface from the plane and estimates what wind speeds are. This instrument has a notoriously rough time in doing so when there’s heavy rain, and since the strongest winds were recorded coinciding with the strongest rain, you can imagine that this region of high wind speed could be suspect. The hurricane hunter mission is still in the storm, so I imagine they will issue a special update if needed. Currently the best estimate of wind speed within the storm is 70 mph. Isaac’s pressure has been dropping today as well and is now 981 mb. Isaac is moving northwest at 12 mph–no change since this morning. Satellite loops show that Isaac remains large, though asymmetric, with most of the strong thunderstorm activity on the west and southwest side. Isaac’s southeast side continues to struggle with dry air and wind shear, which could help to moderate Isaac’s intensity as it approaches the coast.

An oil platform in the northern Gulf of Mexico is reporting sustained winds from the north-northeast at 40 mph this afternoon. A buoy west of Tampa, Florida is recording sustained winds around 30 mph, and platforms south of Louisiana are recording winds from 35-40 mph. The widespread heavy rain of yesterday has lightened up in Florida, but a strong line of thunderstorms in one of Isaac’s outer bands is training northward along and offshore of the east coast of Florida, affecting everyone from Miami to Jacksonville.

This afternoon the AP reported that Isaac’s death toll in Haiti jumped to 19, which puts Isaac’s total death count at 21. It appears most of the deaths in Haiti were due to collapsing structures.

Figure 1. Satellite imagery of Tropical Storm Isaac around 3pm EDT on Monday.

Track forecast:
Models seem to be coming into better agreement today on where Isaac will make landfall, closing in on Louisiana and New Orleans as most likely landfall point. The ECMWF, HWRF, and UKMET all suggest New Orleans as the landfall location. The GFS is only slightly west of that. The GFDL is the farthest west, predicting landfall near the Louisiana-Texas border. Landfall timing remains Tuesday night. Beyond landfall, Isaac is expected to move north toward the Midwest through the rest of this week, however, models are showing that the system will likely slow down around landfall time, prolonging impacts like surge and inland flooding.

Intensity forecast:
The closer Isaac gets to landfall without having formed an eye, the better it is for intensity at landfall. Isaac has strengthened only modestly in the past 24 hours, and is still struggling with a less-than-conducive atmospheric environment. The HWRF remains on the high end of the intensity spectrum, suggesting Isaac will be a weak category 2 upon landfall. Other models suggest it will be a strong category 1, but the difference is splitting hairs. The National Hurricane Center’s official forecast is for Isaac to continue strengthening over the next day, reaching category 2 at landfall.

Figure 2. Tide gauge data from St. Petersburg, Florida. The green line shows the storm surge. As Isaac’s counterclockwise winds blew offshore this morning, water levels feel two feet at St. Petersburg. The winds switched to onshore this afternoon as the center of Isaac moved more to the northwest, bringing a storm surge of two feet to the city.

Storm surge observations from Isaac
This morning, as Isaac’s counter-clockwise winds brought offshore winds to the Tampa/St. Petersburg area, ocean waters fell two feet along the coast. This afternoon, winds have shifted to blow onshore, and a two foot storm surge has been observed at Naples, Fort Meyers, and St. Petersburg on the west coast of Florida. Water levels have also begun to rise along the coast of Louisiana, with a storm surge of 1.5 feet already occurring at Shell Beach on the east side of New Orleans in Lake Borgne.