Impacts Begin Today

Impacts from Hurricane Matthew begin today. You have precious few hours left before conditions become dangerous for travel on the barrier islands. If you live out there and are still on the fence about whether to evacuate, go! You are running out of time. Lane reversals on I-26 end at 10am. You want to be on the road before that.

As today wears on, expect increasing winds to tropical storm force, heavy rainfall, and increasing surge (which will peak tomorrow).

I must reiterate: The time for preparation and evacuation is just about over.

But…it will just be a Category 1!

I’ve seen a lot of focus on Matthew’s classification on the Saffir-Simpson scale on social media, with even a dismissive attitude at times because earlier forecasts saw it weakening to a Category 1 hurricane. This focus is misguided and should not be driving your evacuation decisions because the threat is more than just wind (which even in a Category 1 hurricane is still quite significant) — it’s heavy rainfall on the order of 10"+, storm surge (which may penetrate some 20–25 miles inland along rivers and creeks), and timing of rainfall with high tide. Water is responsible for 75% of hurricane and tropical storm deaths.

Research has shown that the category of a storm on the Saffir-Simpson scale ultimately has no bearing on what kind of surge it can produce. From the National Hurricane Center:

Earlier versions of the Saffir-Simpson Hurricane Scale incorporated storm surge as a component of each category. Storm surge was quantified by category in the earliest published versions of the scale dating back to 1972. However, hurricane size (extent of hurricane-force winds), local bathymetry (depth of near-shore waters), topography, the hurricane’s forward speed and angle to the coast also affect the surge that is produced. For example, the very large Hurricane Ike (with hurricane force winds extending as much as 125 mi from the center) in 2008 made landfall in Texas as a Category 2 hurricane and had peak storm surge values of about 20 ft. In contrast, tiny Hurricane Charley (with hurricane force winds extending at most 25 mi from the center) struck Florida in 2004 as a Category 4 hurricane and produced a peak storm surge of only about 7 ft. These storm surge values were substantially outside of the ranges suggested in the original scale. Thus to help reduce public confusion about the impacts associated with the various hurricane categories as well as to provide a more scientifically defensible scale, the storm surge ranges have been removed from the scale and only peak winds are employed in the Saffir-Simpson Hurricane Wind Scale.

When evaluating your risk, you need to evaluate the entirety of the risk. It is easy to get caught up in the winds — we’re all guilty of it, myself included — but the flash flood threat is a far more dire situation. Depending on where Matthew begins to interact with an approaching cold front, some incredible rain totals could be squeezed out, which would be quite reminiscent of what we went through around this time last October.

It’s the concern over storm surge, heavy rainfall, flooding, and wind working in concert to create significant problems that is driving the evacuation order.

But again, you are running out of time to make preparations and evacuations. By this afternoon, it will be too late.