Maria became the 2nd category five hurricane of the 2017 season, following in the footsteps of historic hurricane Irma whose winds peaked at an astonishing 185 mph.
What exactly does category five mean? For most, it is the absolute benchmark of fear and anxiety when it comes to hurricanes. When you hear category five, you always pay attention – no matter where you live – hurricane zone or not.
The categories assigned to hurricane intensities are for wind and the potential damage that can be caused by that wind. It’s not pressure, not surge, not rain and not size. It’s all about the wind and its damage potential. A category five hurricane is capable of inflicting catastrophic damage – no doubt about it.
However, we must look at the bigger picture to understand the whole of the hurricane – not just its category. We are so fixated on the category yet most people do not understand the rest of the inner workings of the cyclone.
First of all, the hurricane force winds only extend out from the center of Maria up to 30 miles. This is the good news. The bad news is that somewhere within this wind field are extreme winds reaching 160 mph with higher gusts. The recon plane and the instruments used to measure wind and pressure cannot be everyone all at once – the convection changes, thunderstorms go up, then they go down; it is very dynamic inside the core of an intense hurricane. Luckily for us mere humans, the radius of maximum winds, in the case of Maria, is fairly small. This means that it will take a direct hit of the core to bring those unimaginable winds to any specific location. Obviously, this happened with Irma and again last night with Maria in the case of the island of Dominica.
The other aspect that gets lost when thinking of hurricanes solely by their category is the immense threat from rain and the resulting floods. If ever there was a lesson in this in recent times it was Harvey in Texas.
Harvey was an exceptional situation where by the storm slowed down and virtually stalled over the region – this led to the historic rain fall totals that exceeded 4 feet in many locations.
As for Maria, the slow movement is a problem but its the island of Puerto Rico itself that poses the biggest issue in terms of rain. Puerto Rico has mountains and those mountains are lined with beautiful tropical river systems that run through valleys and eventually reach the sea. What do you think is going to happen when 10, 15 or 25 inches of rain falls on those mountains in short order? Is there a category for that? No. If there was, it would also be a five in my opinion. The flood threat from Maria for the people, places and things in Puerto Rico is exceptional and I am very concerned about it. The wind will grab the headlines but the rain could be what Maria is ultimately remembered for. We shall see.
RAINFALL: Maria is expected to produce the following rain accumulations through Thursday: Central and southern Leeward Islands...10 to 15 inches, isolated 20 inches. U.S. and British Virgin Islands...10 to 15 inches, isolated 20 inches. Puerto Rico...12 to 18 inches, isolated 25 inches. Northern Leeward Islands from Barbuda to Anguilla...4 to 8 inches, isolated 10 inches. Windward Islands and Barbados...2 to 4 inches, isolated 6 inches. Eastern Dominican Republic...4 to 8 inches, isolated 12 inches.
I have prepared a video discussion this morning emphasizing the point about the small hurricane force wind area within Maria’s core. I will have another video update posted this afternoon after the 5pm NHC advisory package is released.