Question of the
Month - September, 2003
If hurricane season runs from June 1st through November 30th, why is
September considered to be peak hurricane season for Delaware?
Although the official hurricane season for the Atlantic basin runs from 1 June to 30 November, tropical cyclones can occur in any month. In fact, this year's Tropical Storm Ana originated in April, developing as a sub-tropical system on April 20th, and becoming an officially named tropical storm on April 22nd. However, research (Landsea, 1993) has shown that historically, 97% of tropical activity in the Atlantic basin occurs during the June through November time frame.
The primary time period for development of tropical storms in the northern hemisphere is late summer and early fall, with maximum tropical storm and hurricane activity typically occurs in early to mid September. This early autumn peak of storm activity is a result of the three primary factors necessary for tropical storm development: (1) warm ocean waters (80o F or greater) that provide evaporation and "fuel" for the storm; (2) a pre-existing weather disturbance, with moist, unstable air that contributes to thunderstorm development; and (3) light winds in the upper atmosphere that allow tropical storms to become well developed.
This diagram, provided by NOAA, shows the average number of storms occurring
during each month of hurricane season. There is a noticeable peak in tropical
storm and hurricane activity from mid-August through mid-October, with
the greatest number of storms occurring in mid-September.
While
the peak period of summer and associated solar radiation occurs in late
June in the Northern Hemisphere, there is a time lag before the oceans
to reach their maximum temperatures. Off the coast of Delaware, ocean
water temperatures are warmest in the fall (September) because of the
influence of the Gulf Stream current which migrates northward along our
coast through the summer months.
Before peak hurricane season arrives, it's best to prepare in advance
for the likelihood of high winds, high tides, torrential rainfall, and
flooding that can occur with a tropical storm or hurricane:
- Know the hurricane risk for your area
- Learn location of evacuation routes and shelter areas
- Review your insurance policy
- Have a Family Disaster Plan for yourself and your pets
- Assemble a Disaster Supply Kit
- Listen to NOAA weather radio (purchase a battery operated radio)
A Watch issued for your part of the coast indicates the possibility that you could experience coastal storm or hurricane conditions within 36 hours. This watch should trigger your family's disaster plan, and protective measures should be initiated - especially those actions that require extra time such as securing a boat, leaving a barrier island, etc.
A Coastal Flood Warning issued for your part of the coast indicates that moderate or severe coastal flooding is occurring, is imminent, or is expected within the next 12 hours.
A Hurricane Warning is issued when sustained winds of at least 74 mph are expected within 24 hours. Once this warning has been issued, your family should be in the process of completing protective actions and deciding the safest location to be during the storm.
If a tropical storm threatens your area, listen to the advice and instructions issued by local officials. For more information on disaster preparedness, contact your local emergency management agency, or DEMA
(302-659-3362).
Visit the following websites for additional information:
Delaware Emergency Management Agency (DEMA)
Federal Emergency Management Agency (FEMA)
National Hurricane Center (NHC)
