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Evacuation Information EVACUATION TIMELINE
Probabilities of Hurricane Conditions
The probability that a storm will actually make landfall or at least pass close enough to Chatham County to endanger lives and property (i.e., the eye will come within 65 miles) is expressed a percentage around the official forecast track of a storm up to 72 hours or more into the future. They are provided every six hours and are useful in assessing the potential threat to a particular location along the coast as the storm approaches. However they can be mistakenly over relied on as the primary criteria in deciding if an evacuation is warranted. While common sense dictates that there must be some reasonable probability of a direct hit to justify any evacuation decision, there is no objective standard for determining what specific level of probability might constitute an acceptable or unacceptable risk to the community.
The Chairman and Mayors will have to collectively (and somewhat subjectively) agree on a minimum threshold probability level for approving any evacuation order (especially Mandatory). Ideally consensus will be reached in advance of a "decision point" so that a subsequent evacuation decision can be made in time to satisfy the County's clearance time requirements. The theoretical probabilities for a direct hit at any given location over time are:
Eye of Storm 72 Hours Out----------------10% Probability
Eye of Storm 48 Hours Out--------------13-18% Probability
Eye of Storm 36 Hours Out--------------20-25% Probability
Eye of Storm 24 Hours Out--------------35-45% Probability
Eye of Storm 12 Hours Out--------------60-70% Probability
It is extremely unlikely that the probability of a hurricane strike will ever exceed 25-35% at the "decision point" required to make a timely evacuation decision. It will be virtually impossible to have as much as a 50% probability at that time, if the gale force winds arrive seven hours or more before the eye. Therefore any evacuation order will almost always have to be issued while uncertainty is still relatively high. Delaying a decision to evacuate past the appropriate decision point when the probability is better than 50-50 will be too late, even for a Category 1 or 2 storm.
Phased Evacuations
Click on image for full size table.
The decision to evacuate (and if so, to what degree) is complex, difficult, politically sensitive and personally stressful. This is especially true when time is of the essence, a high level of uncertainty exists, and the negative consequences of an incorrect decision are great. It is equally traumatic and potentially confusing for citizens to be informed of an evacuation order (particularly a Mandatory one) with little or no advance notice, insufficient lead time to make last minute preparations and virtually no luxury of being able to respond at a leisurely pace. Therefore if circumstances and time permit every effort will be made to "phase in" the levels and types of evacuation to permit emergency operations personnel and citizens alike to prepare and respond, and to minimize roadway congestion and traffic control problems.
Prior to any evacuation decision-making meetings CEMA will prepare a proposed evacuation schedule for implementing any resulting evacuation in phases. The exact nature of the schedule (or timetable) will vary based on the speed and intensity of the storm, the immediacy of the threat, the times of day involved, and the levels and types of evacuation considered.
If the threat of the storm diminishes over time the entire schedule may not have to be carried out. However if the storm increases speed or strength rapidly or unpredictably some portions may have to be time compressed or even eliminated altogether in favor of an immediate Mandatory County-wide evacuation. In any event every effort will be made to coincide the schedule with the periodic issuance of Advisories (at 11:00 and 5:00) and consideration for clearance time requirements.
