NHC upgrades Sandy to a Cat 3 in reanalysis, affirms changes needed for warnings

The National Hurricane Center released their final analysis of Hurricane Sandy this week. At 157 pages and 14 Mb, it's by far the largest tropical cyclone report NHC has ever released (previous record: 55 pages from Hurricane Ike of 2008.) NHC upgraded Sandy to a Category 3 hurricane in post-analysis. Data from the Hurricane Hunters showed that Sandy had 115 mph sustained winds at landfall in Cuba, making Sandy the second major hurricane of the 2012 season (Michael was the other.) NHC's report reaffirmed that Sandy was not a hurricane when it made landfall in New Jersey, having transitioned to a post-tropical cyclone when it was 2.5 hours and 50 miles away from landfall. Sandy officially made landfall in New Jersey as a post-tropical cyclone with sustained 80 mph winds and a central pressure of 945 mb. However, Sandy did bring hurricane force sustained winds to the coast before transitioning to a post-tropical cyclone. Great Gull Island, New York, between Long Island and Fishers Island, measured a 1-min mean wind of 75 mph at an elevation of 18 m (59') at 4:35 pm EDT on 29 October, about 25 minutes before Sandy lost its status as a hurricane. NHC noted: This observation suggests that sustained hurricane-force winds likely occurred onshore over a limited area while Sandy was still a hurricane.


Figure 1. Hurricane Sandy at 10:10 am EDT October 28, 2012. Image credit: NASA/GSFC.

Sandy was responsible for 72 direct deaths in the U.S., the second highest toll from a U.S. hurricane since Hurricane Agnes of 1972 (Hurricane Katrina of 2005 was the highest, with at least 1500 direct deaths.) Sandy's storm surge was responsible for most of the U.S. deaths--41 of the 72 fatalities (57%). Falling trees during the storm killed twenty people, a rather high number that again highlights that hazard in the northeastern and mid-Atlantic states, even in locations experiencing winds of less than hurricane force. At least 87 deaths, an even greater number than for direct deaths, were indirectly associated with Sandy or its remnants in the United States. About 50 of these deaths were the result of extended power outages during cold weather, which led to deaths from hypothermia, falls in the dark by senior citizens, or carbon monoxide poisoning from improperly placed generators or cooking devices.

Sandy by the numbers: some statistics from NHC's final report on Sandy:

Death toll: 147 (72 in the U.S., 54 in Haiti, 11 in Cuba)

U.S. Damage: $50 billion, second costliest hurricane of all-time

Cuban Damage: $2 billion, fourth costliest hurricane of all-time

Haitian Damage: $0.75 billion, costliest hurricane of all-time

Homes damages/destroyed: 945,000 (650,000 in U.S.)

Power outages: 8.5 million U.S. customers, 2nd most for a natural disaster behind the 1993 blizzard (10 million)

Maximum sustained winds measured: 93 mph at Cabo Lucrecia, Cuba

Maximum U.S. sustained winds measured: 75 mph at Great Gull Island, New York

Peak U.S. wind gust: 95 mph at Eaton's Neck, Long Island, NY (24 m elevation)

Maximum U.S. storm surge: 12.65', King's Point, NY, west end of Long Island Sound

Maximum U.S. Storm Tide (measured above MLLW): 14.58', Bergen Point, NJ

Maximum Storm Tide at The Battery in New York City: 14.06'. This is 4.36 ft higher than the previous record set in December 1992, and 4.55 ft higher than in Tropical Storm Irene in 2011.

Maximum significant wave height: 33.1' at the buoy east of Cape Hatteras, NC (2nd highest: 32.5' at the Entrance to New York Harbor)

Maximum rainfall: 28.09", Mill Bank, Jamaica

Maximum U.S. rainfall: 12.83", Bellevue, MD

Maximum snowfall: 36", Richwood, WV and Wolf Laurel Mountain, NC

Minimum pressure: 945.5 mb, Atlantic City, NJ at 7:24 pm EST, October 29, 2012. This is the lowest pressure measured in the U.S., at any location north of Cape Hatteras, NC (previous record: 946 mb in the 1938 hurricane on Long Island, NY)

Destructive potential of storm surge: 5.8 on a scale of 0 to 6, highest of any hurricane observed since 1969. Previous record: 5.6 on a scale of 0 to 6, set during Hurricane Isabel of 2003.

Maximum diameter of tropical storm-force winds: 1000 miles, highest for any Atlantic tropical cyclone on record, going back to 1988.

Diameter of ocean with 12' seas at landfall: 1500 miles


Figure 2. Snowfall from Superstorm Sandy hit 36" at locations in West Virginia and North Carolina.
Image credit: NOAA/HPC.

Questions on NHC's handling of warnings for Sandy
In the Sandy report, NHC documents that their forecasts of Sandy's track, intensity, and storm surge were all excellent, largely beating the average error margin for forecasts for tropical cyclones made during the previous five years. However, NHC has been criticized for electing not to issue hurricane warnings in advance of Hurricane Sandy for the U.S. Sandy was expected to transition to a non-tropical system before landfall, and NHC opted days in advance to issue high wind warnings and not hurricane warnings for the U.S. It is quite possible that NHC's decision not to put up hurricane warnings cost lives, since the public pays far more attention to hurricane warnings than any other type of wind warning (except tornado warnings.) In the Sandy report, NHC argues that "Intentionally misrepresenting Sandy as a hurricane would have severely damaged the credibility of the NWS and undermined its ability to serve the public for years to come." Another option to properly call Sandy post-tropical but put up hurricane warnings for the coast was also considered, but "a procedure for disseminating post-tropical advisories with tropical warnings had never been developed, tested, or publicized, and the NWS feared that hurriedly crafting and implementing untested procedures could easily break automated vendor software and disrupt the flow of information to users at a critical moment." The report acknowledges that due to the unique situation posed by Hurricane Sandy, a change to the hurricane warning definition is needed. They propose: The hurricane warning definition would be broadened to apply to systems after their tropical cyclone stage has ended, thus allowing hurricane or tropical storm watches and warnings to remain in effect for post-tropical cyclones. In addition, the NWS would ensure the continuity of service in any situation by allowing the NHC to issue advisories through the post-tropical cyclone stage as long as the system poses a significant threat to life and property. A second proposal: "set a target date of 2015 for NOAA to implement explicit storm surge watches and warnings, a goal NOAA has been working toward for several years. Multiple studies have shown significant confusion on the part of the public regarding their storm surge risk, and highlighted the need for improved communication of this hazard. With the implementation of a storm surge warning, the NWS will warn explicitly for the phenomenon that presents the greatest weather-related threat for a massive loss of life in a single day." Both of these changes are ones I hope get adopted as soon as practical, as the warning information given to the public during Sandy could have been much better, potentially saving lives and property.

Spectacular NOVA show tonight: Earth From Space
The PBS NOVA series is airing a two hour special tonight (Wednesday), called "Earth From Space", a spectacular new space-based vision of our planet. The promo on the website advertises: Produced in extensive consultation with NASA scientists, NOVA takes data from earth-observing satellites and transforms it into dazzling visual sequences, each one exposing the intricate and surprising web of forces that sustains life on earth. Viewers witness how dust blown from the Sahara fertilizes the Amazon; how a vast submarine "waterfall" off Antarctica helps drive ocean currents around the world; and how the Sun's heating up of the southern Atlantic gives birth to a colossally powerful hurricane. From the microscopic world of water molecules vaporizing over the ocean to the magnetic field that is bigger than Earth itself, the show reveals the astonishing beauty and complexity of our dynamic planet. It should be a great show!

Jeff Masters