DEEP: Coastal Hazards Primer - Tropical Storms and Hurricanes

Coastal Hazards Primer - Tropical Storms and Hurricanes
 
 
 
Terminology
Hurricanes, tropical storms, and tropical depressions are different categories of tropical cyclones. The National Weather Service defines tropical cyclones as "…nonfrontal, low pressure synoptic scale (large scale) systems that develop over tropical or subtropical water and have definite organized circulations. Tropical cyclones are categorized based on the speed of the sustained (1-minute average) surface wind near the center of the storm. These categories are: Tropical Depression (winds less than 34 knots/39 mph), Tropical Storm (winds 34-63 knots/39-74 mph), and Hurricanes (winds at least 64 knots/74 mph)."

Hurricanes are further classified by the familiar Saffir-Simpson scale:

  • Category 1: sustained winds between 74-95 mph
  • Category 2: sustained winds between 96-110 mph
  • Category 3: sustained winds between 111-130 mph
  • Category 4: sustained winds between 131-155 mph
  • Category 5: sustained winds greater than 155 mph

It’s natural to assume the higher the category, the worse a storm; however, one must also realize that these are relative terms, because lower category storms can sometimes inflict greater damage than higher category storms, depending on where they strike and the particular hazards they bring.18

The Tropical Storm and Hurricane Threat in Connecticut
The Connecticut Department of Emergency Services and Public Protection (formerly DEMHS) considers a strong Category 3 hurricane the most probable, worst-case natural disaster scenario.19   When compared to the hurricanes that impact the US southeast coast and Gulf of Mexico, it’s easy to think the threat to Connecticut is minimal. However, here is a summary of the major tropical cyclones that impacted Southern New England in the 20th and 21st centuries.

Historic Hurricanes and Tropical Storms20

Name

Date(s)

Intensity

Unnamed

7/21/1916

Category 1

Unnamed

9/21/1938

Category 3

Unnamed

9/14-15/1944

Category 3

Carol

8/31/1954

Category 3

Edna

9/11/1954

Category 3

Connie

8/11-12/1955

Tropical Storm

Diane

8/18-20/1955

Tropical Storm

Donna

9/12/1960

Category 2

Belle

8/9-10/1976

Category 1

Gloria

9/27/1985

Category 2

Bob

8/19/1991

Category 2

Bertha

7/12-13/1996

Tropical Storm

Floyd

9/18/1999

Tropical Storm

Irene 8/28/2011 Tropical Storm

Hurricane of 1938 aka "The Long Island Express"/"The Great New England Hurricane": The hurricane of 1938 was the deadliest disaster in the history of Connecticut and New England in general.  A brief is quoted directly from an authoritative document on the storm, Hurricane Floods of September 1938 (1940):

"During the brief interval of 6 hours on September 21, 1938, a West Indian hurricane passed over Long Island and New England.  The hurricane as it struck New England was the climax of a 4-day period of rainfall which in itself was of outstanding amount and character and which produced river stages that inundated and damaged nearly everything on the river flood plains.  When measured by the appalling loss of life and property by the combined forces of the hurricane winds and the associated ocean storm waves and river floods, these events constituted the greatest catastrophe in New England since its settlement by the white man."

The 1938 hurricane, a strong Category 3, killed 125 people in Connecticut, making landfall at high tide with winds up to130 mph and generating a storm surge up to 12 feet high.  The damages in Connecticut were estimated at $53 million (1938 dollars).  Property damage on the coast of Connecticut was $22 million (1938 dollars).

To help understand the level of impact, the Connecticut State Library has 132 aerial photos taken shortly after the Hurricane had passed.

The Hurricane of 1944: The hurricane of 1944 hit Long Island and Connecticut as a Category 3 hurricane.  Injuries, deaths, and damages were less than in the 1938 hurricane due to better warnings and fewer structures because of a lack of rebuilding from the 1938 hurricane.  Nevertheless, seven people were killed and damages were between $3 million and $5 million (1944 dollars).21

Hurricane Carol (1954): On the morning of August 31, 1954 Category 3 Hurricane Carol arrived shortly after high tide, causing widespread flooding and killing 65 people. Storm surge levels ranged from 5 to 8 feet across the west shore of Connecticut and from 10 to 15 feet from the New London area eastward. Rainfall amounts ranged from 2 to 5 inches across most of the area with the heaviest amounts, up to 6 inches, in the New London. Strong winds also devastated crops in the region. Nearly 40 percent of apple, corn, peach, and tomato crops were ruined from eastern Connecticut to Cape Cod.22

Hurricane Edna (1954): Although this particular hurricane did not directly strike Connecticut (it made landfall around Martha’s Vineyard and Nantucket,) it nevertheless caused damage to southeastern Connecticut in areas that were already impacted by Hurricane Carol the month before. Between the two storms, rainfall totals for Connecticut were 5 to 7 inches west of the Connecticut River and up to 11 inches along the southeastern coastline.23

Tropical Storms Connie and Diane (1955):The remnants of hurricanes Connie and Diane occurred in early August 1955.  Despite not making landfall in Connecticut as proper hurricanes, they bear mentioning for this reason: "… their combined maximum rainfall of 27 inches caused catastrophic flooding in western Connecticut."  Refer back to the section on Flood Hazards to see the details of the 1955 Flood events.24

Hurricane Donna (1960): Hurricane Donna made landfall in Connecticut September 12, 1960. Wind gusts off of Block Island, RI., were recorded at 130 mph, with sustained winds of 95 mph, and storm surges along the New England coastline ranged from 5 to10 feet. Donna is the only hurricane on record to produce hurricane force winds in Florida, the mid-Atlantic, and New England combined.25

Hurricane Gloria (1985): The last hurricane to directly strike Connecticut was Gloria in 1985.  Gloria was a Category 2 hurricane when it made landfall at Westport, but relatively light rains and low tide upon landfall resulted in very little flood damage compared to storms from earlier in the century.  The peak surge at New London Harbor was approximately 5.8 feet.  Had this occurred at high tide, flooding would have been much greater.26

Hurricane Bob (1991): Connecticut received an indirect strike from Hurricane Bob in August of 1991. The bulk of the storm hit Newport, RI., but hurricane force winds were recorded as far west as the Connecticut River. The heaviest rainfall of over 7 inches affected western Rhode Island and extreme eastern Connecticut and despite being primarily localized to the east, Bob was responsible for six deaths, all in Connecticut.27

Tropical Storm Irene (2011): On August 28, 2011 Connecticut was hit by Tropical Storm Irene, the remnants of Hurricane Irene that formed a week earlier.  Despite weakening to Tropical Storm levels, Irene severely damaged or destroyed over 300 homes, and caused widespread coastal flooding.  At storm's end, approximately half the state was left without power, and many rural areas had to wait over a week for it to be restored.   

The National Weather Service Forecast Office for Boston, a source for much of the information provided above, is a useful source of information on New England Hurricanes, including descriptive information, historical perspectives, and safety tips.

Hurricane Response and Recovery in Connecticut
The State Natural Disaster Plan (2009) is a blueprint for hurricane response and recovery. The plan defines the roles of state agencies, local municipalities, and private entities, and explains how the State Emergency Operations Center (EOC) oversees the response effort. Several pertinent facts include:

  • In any type of disaster or emergency, state agencies must first fulfill departmental mandates established by state statutes, regulations or executive orders and then provide support to local authorities. Exceptions are made only in cases of imminent peril to life and health.
  • If necessary, the Governor may declare a state of emergency under Connecticut General Statutes Section 28-9, and invoke extensive emergency powers to take any action reasonably necessary in light of the emergency. These emergency powers include (but are not limited to) taking operational control of all civil preparedness forces and functions, modifying or suspending statutes and regulations, ordering evacuations, removing debris from public and private land or waters, and seizing property.
Identifying and measuring storm threats
Hurricane response starts with the National Weather Service (NWS). For coastal New England, any tropical cyclone that is near the Bahamas becomes closely watched. Once these become a threat to Connecticut, the NWS begins working closely with DESPP. The NWS uses the SLOSH model to estimate coastal flood damages according to the latest weather data and will issue coastal flood watches and warnings according to their analysis of the threat. Hurricane Watches and Warnings are differentiated as follows:
  • HURRICANE WATCH: An announcement that hurricane conditions (sustained winds of 74 mph or higher) are possible. within 48 hours in of the anticipated onset of tropical-storm-force winds.
  • HURRICANE WARNING: An announcement that hurricane conditions (sustained winds of 74 mph or higher) are expected within 36 hours in of the anticipated onset of tropical-storm-force winds.28

How evacuation orders are decided
The State Natural Disaster Plan defines how DESPP should communicate with the National Hurricane Center (NHC) and local NWS offices to discuss evacuations. It also sets forth protocols for communication between the NWS, DESPP and municipal officials before and after an evacuation recommendation or order is issued, and the responsibilities of DESPP to notify media and federal, state, private agencies.

The section of the Natural Disaster Plan that defines coastal evacuation policies and procedures is based on information from the 1994 Connecticut Hurricane Evacuation Study: Technical Data Report. This established the general rule that it takes seven hours from the time residents receive official notification to evacuate. An additional two hours must be added to account for the time it takes to notify the public to evacuate. Therefore, a total of nine hours is required for coastal evacuations.

The Connecticut Hurricane Evacuation Study also provides a "Decision Arc Method," which combines information about possible storm tracks and speeds, potential inundation and evacuation areas, and estimated evacuation times and routes. For example, with a nine-hour estimated evacuation time and a hurricane headed for Connecticut at 30 knots (~34.5 mph), the "decision arc" for this hurricane occurs where the leading edge of the storm system reaches 270 nautical miles (310.7 miles) from the estimated point of landfall.

If the NHC does not issue a hurricane warning for the Connecticut coastline DESPP will not make evacuation recommendations. In these cases, evacuation decisions are made by local officials based on information from NWS. 

In Summary
What can you do when it comes to the threat of hurricanes in Connecticut?

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Content Last Updated January 3, 2012