Every profession has its own terminology, and it often seems to outsiders that doctors, chemists, physicists, and even meteorologists just use those obscure terms to sound important. That’s not the reason (your reporter is a physicist.) Professionals use terms which have very specific meanings, not general definitions.

For example, in science, the seemingly interchangeable terms theory and hypothesis have different meanings. The phrase “it works in theory but not in practice” is meaningless to a scientist because if it doesn’t work in practice, it isn’t a theory.

Most of the time terminology isn’t important to the layperson, but if hurricane Irma is headed toward you, it is important to understand the real meaning of scientific terms.

Category 4 or 5

The first and probably most important hurricane terminology you need to understand is just what it means that a storm is a category 4 or a category 5. Some people in Florida are telling reporters that since Irma has been downgraded from a category 5 to a category 4 storm means that they were right in deciding to ride it out.

Nothing could be further from the truth. The sustained winds near the eyewall of Irma are 155 mph. A category 4 storm has sustained winds of 130 to 156 mph. In other words, there is currently a two mph wind speed difference from Irma becoming a category 5 hurricane.

Further, since Irma is also moving to the north west at 14 mph, on one side, you subtract that from the sustained wind speed and on the other, you add the 14 mph.

Look at it this way, if you drive your car into a solid wall at 90 mph, the damage won’t be significantly different than if you are only traveling 88 mph.

Storm surge

That is another confusing term which is easily understood. Essentially storm surge is just water being pushed ahead of the wind and will hit land before the maximum winds reach land. In portions of the lower east coast of Florida, the storm surge will add up to ten feet above what ever the current height of tide is.

The difference between high and low tide is less the further south you go, so while in Boston it might be 6 feet on an average day, in Miami the range from low tide to high tide is about 3 feet.

Think of blowing on hot coffee, the ripples on the surface are cup sized storm surge.

High tides in Miami will occur at about noon and midnight. These change daily, but those will be the approximate times. For the next several days.

With a storm the size of Irma, the storm surge will likely last for a full change of tide from low to high.


You will hear that term a lot and, again, it is easy to understand. Hurricanes have increasing wind speeds from the outer edge to the edge of the eye, that calm space in the center of a well-organized hurricane.

The eyewall is simply that edge between the maximum wind and the virtual calm of the eye.

Computer models

You will hear about two different computer models - that is predictions made based on decades of weather knowledge distilled into computer programs which tell scientists where a storm is likely to head and how strong it will be.

With climate change increasing the temperature of the ocean beyond that of the past several thousand years these models are constantly being modified.

The two basic models being used are the European and U.S. models. The European model is more complex and takes about 6 hours to produce after it is fed a new set of data from the hurricane hunter airplanes. The U.S. model takes about an hour less running on the fastest supercomputers available.The two models are almost identical at this time after several days when each new set of calculations brought them closer and closer together.

There is no longer any question of whether Irma will hit nearly all of Florida.

The four best forecast models are ECMWF, GFDL, GFS, and UKMET and all four are what are termed, global dynamical models. That is, they calculate the weather predictions for a very large area, as opposed to the National Weather Service’s NAM or North American Model which is much faster because it focuses on a very small portion of the world. NWS also has the GFS or Global Forecast System model which is a global model.

When you hear about the U.S. vs. European model, they are referring to the GFS and ECMWF models.

The ECMWF: The European Center for Medium-Range Weather Forecasting (ECMWF) model is considered the best model for general weather forecasting in the middle latitudes.

GFDL: The NWS/Geophysical Fluid Dynamics Laboratory model predicts intensity as well as the path.

HWRF: The NWS/Hurricane Weather Research Model. HWRF is a very advanced atmospheric physics model including the atmospheric conditions along with ocean conditions such as temperature and waves.

UKMET: The final global model is from the meteorological office in the United Kingdom. The others are on the internet, but UKMET is a subscription only model.

NOGAPS is a U.S. Navy model which doesn’t work very well. There are also statistical models which do not use detailed measurements and are not computationally complex.

There are also statistical models which do not use detailed measurements and are not computationally complex.

As of Friday the major models only differ by a few miles, and all show that the entire state of Florida could be covered by Irma at the same time.

For the mathematically inclined I believe the last time I looked at these models in detail they required solving about 200 simultaneous equations, each dependent on the others and using thousands of pieces of data.