Interpreting Hurricane Forecasts for the Public Health Sector with Application to Other Severe Storms 

John Gaynor
NOAA Research

And

Margaret Fowke

National Weather Service 

If you need further assistance with interpreting weather information presented here, contact your local weather forecast office for assistance. 

http://www.nws.noaa.gov/organization.php

Introduction:  How does weather information connect to health?  Does it make a difference? (Slide 1)

Many clinicians and health professionals understand the importance of prevention.  However, using weather forecasts as a tool in prevention of health issues and aid in medical planning is generally not well understood within the health sector. This CPR lesson focuses on hurricanes.  Hurricanes forecasts, watch, or warnings can provide clearer explanations of further consequences such as fresh water vs. salt water flooding, lightning, tornadoes, storm surge, and rip currents which have numerous public health impacts. Following are just a few examples of the hurricane forecasts connected to public health.   Prior to hurricane season, medical/health communities can begin planning to order medical supplies, staffing for evacuating critically ill, routine emergency drills etc. Three to four days prior to landfall focusing on interpreting hurricane tracks and probabilities can be very useful in reducing public health impacts such as food/water/medications issues due to power loss and/or flooding, limited access to emergency medical care due to debris, flooding, downed power lines and other damage.  Continuous lightning strikes can result in cardiac arrest and drowning from high rising flood waters.  These offer just a small sketch but during the presentation we will address others.

Watches and Warnings (Slide 1)

For hurricanes, watches can be posted three or four days in advance of forecasted landfall in the region in which landfall is possible.  During a hurricane watch, any provisions that are need such as more drinkable water, food not requiring refrigeration, fresh batteries, fuel for the vehicle, should be quickly purchased and perhaps, one might begin to board or tape windows.  Longer term preparations should have already been made, but there is time to replenish stocks. You should follow the weather forecasts for any changes.

A hurricane warning is posted anytime from 12 hrs down to 1.5 days in advance of the predicted start of hurricane force winds.  By the time of the issuance of a warning, you should have needed supplies already in hand.  Boarding of windows should be completed and anything that may blow away should be brought inside.  Then you should go inside and prepare a place in the strongest part of the home, preferably in an interior small room with no windows, such as a bathroom.  If you have been ordered to evacuate, follow those orders.  If not, do not evacuate and clog up the highways for those who must get out.

Severe thunderstorm watches are usually issued 12 hours down to a few hours in advance of a predicted storm in you area.  Usually, there will not be adequate time for provisions so you should already be prepared for loss of power.  Continue to follow the forecasts closely for any changes.

Severe thunderstorm warnings means the storm is imminent.  You must get inside shelter immediately and stay away from windows.  Make sure you windows are closed.  Open windows can increase damage to your home.

Tornado watches are also issued from 12 hours down to a couple of hours in advance.  You prepare for these watches as you would for a severe thunderstorm.  A tornado warning means that a tornado has been sighted, either by a person or by radar.  Therefore, when a tornado warning is issued, you must take action immediately.  Make sure to close the windows and move the strongest portion of the house, away from windows.  A basement is best.  If you do not have a basement, a small interior room such as a bathroom is the best place.

Understanding the Hurricane Cone of Uncertainty  (Slide 2)

The National Weather Service runs computerized hurricane models as do some universities in the US and weather centers in other countries.  These models predict the track and intensity of the hurricane, but there is uncertainty in these predictions.  To display this uncertainty, the Weather Service creates a distribution of the predicted tracks of the eye of the hurricane which is represented by the cone of uncertainty.  In a normal distribution represented by a bell-shaped curve, the center of that distribution indicates a higher probability of the hurricane eye passing over a particular spot.  In the case of the cone of uncertainty, there is a significant chance that you will experience the effects of the hurricane anywhere in the cone. This is due to the fact that the hurricane as a certain size and hurricane force winds and heavy rains can extend well beyond the eye.

The large dots with a date and time on the center line of the cone indicate the approximate predicted time and date of the passage of the hurricane eye.  This is not the time and date when the storm will begin.  Depending on the size of the storm, you will experience several hours of hurricane conditions before this estimated time of eye passage.  You must subtract several hours from this time and use that time as the point when you need to complete preparations and be inside or evacuated if asked to do so.

Hurricane Structure – What you need to know to protect yourself  (Slide 3-5)

Hurricanes are not symmetric about the eye and come in different sizes.  There is no correlation between the size of a hurricane and its strength.  Usually, the strongest part of the hurricane is in its right front quadrant when oriented in the direction of the movement of the hurricane.  These facts, in addition to the strength of the hurricane, are taken into account when authorities consider where to evacuate.  Also the type and location of buildings are also taken into account.  For example, occupants of a manufactured home would be more likely to be asked to evacuate than occupants of a more substantially constructed home and these two structures may be only blocks from each other.

It is critical to understand the spiral bands of a hurricane are where the “action” is.  Embedded within these bands is the heaviest rain, strongest winds, continuous lightning and possible tornados.  Between the bands, the conditions are less severe.  Therefore, a hurricane does not represent continuous very strong winds and heavy rain.  This makes it impossible for you to know when the storm is definitely passed.  You must monitor your radio and rely on the experts to tell you when it is over in your area and it is safe to go outside. They have the data and knowledge. The worse situation would be if you were to go outside to check on neighbors or damage and another band moves through with hurricane conditions, placing you at risk.

Having the experts tell you when the storm is over also applies to severe thunderstorms.  They also often have a complex structure.  One severe cell of a storm may move over you and the conditions may calm somewhat, only to be followed by another severe cell.

During the last 10 to 15 years, more people have died in hurricanes from coastal and inland fresh water flooding than from the storm surge.  This is because the Weather Service does a good job, in most cases, of predicting the location and size of a storm surge (that can easily exceed 20 ft), but the prediction of exactly where the heavy rains will fall and where the flooding will occur remains a challenge.

Be Prepared (Slide 6)

When asked to evacuate by authorities, follow their directions.  Evacuation orders are not given lightly.  Authorities must balance the risk of people staying in place versus the risk of the process of evacuation (auto accidents or moving into potential flood zones).  Although the authorities may issue mandatory evacuations, they cannot force you out of your home.  They do try hard to convince you.  Mandatory evacuations should be taken extremely seriously.  In these cases, authorities believe that people are at extreme risk to their lives if they remain.

Many health facilities are built along the coasts at risk for hurricanes and within potential storm surge areas.  Health official working in or responsible for these facilities should know the procedures for evacuation of patients because, in the event of a storm surge, the facility may be unusable for days to weeks after the storm.  Likely the first one or two floors to the facility will be flooded, assuming the building itself can withstand the forces of the water and wind.  In the event that there is not time to evacuate everyone, these facilities must have water, food and power to last days to, perhaps, two weeks.  In potential storm surge or flood areas, power supplies such as generators should never be placed on the first floor of the building, let alone in the basement.  Nor should critical supplies such as blood or medications be placed on these floors. Expect them to be flooded after a storm.

It is most important to continuously monitor weather updates on the radio while in a watch or warning.  Conditions can change rapidly.  The best place for forecasts of potentially hazardous weather conditions is the National Weather Service (NWS).  Although they do provide daily weather forecasts under normal conditions, their mission is to save lives and property. Therefore, they are specifically tuned to provide forecasts of extreme weather such as hurricanes and severe thunderstorms.  You can find forecast directly from the NWS on the NOAA (noaa.gov) website after clicking on the National Weather Service on the lower right hand side of the page and then typing in your local weather forecast office from which your local forecasts originate.  It is highly recommended that you buy a NOAA weather radio, available at most electronic stores for as little more than $20.  This radio runs on batteries, of course, and provides continuous daily forecasts.  More importantly, it alerts you to watches and warnings.  If there is a warning in your area and you have the radio turned off, it automatically turns on with a loud noise with the warning and suggestions of what you should do.   This is particularly useful when you are asleep.  Finally, your public radio channel provides forecasts directly from the NWS.  However, warnings and watches may be somewhat delayed in time compared to the website or NOAA weather radio.  Other media outlets provide forecasts from private forecasting companies and most pass the NWS watches and warnings through to you.  However, at times, the private forecasters interpret this information provided by the NWS.  Different interpretations may cause confusion which can be dangerous in a high weather risk situation.  Clarity, reliability and consistency are critical in these situations.

Immediately After the Storm (Slide 6)

Do not go outside until the officials have told you that the storm is over in your area.  When you do, our first inclination is to start cleaning up or helping others do so.  You must remember that the roads in your area may not be passable for hours or even days due to debris from structures and trees or due to flooding.  You may be doing tasks that you do not normally perform, increasing your risk of injury.  Remember to be very careful because it is likely that you will not be able to receive emergency medical assistance for quite awhile if you are injured.

The old adage, prepare for the worst and hope for the best, is very applicable when it comes to severe weather.  Understanding what the forecasts are telling you and being prepared will help save you and those for whom you are responsible.