Irma Getting Ever So Closer

Hurricane Irma is formidable Category 3 hurricane with 125 mph 200 km/h 109 knot winds. It has a central pressure of 933 millibars. It is moving slowly west at 9 mph. Irma should turn northward later tonight. South Florida and Florida Keys are feeling the affects of Irma.

There are feeder bands pelting South Florida with heavy rain and tropical storm force winds. Irma is a large hurricane despite weakening to Category 3.

Cuba is still experiencing hurricane force winds. Hurricane force winds are up to 138 miles 221 km 120 nautical miles across from northwest to northeast quadrant and northeast to southeast quadrant. Tropical force winds are up to 380 miles 608 km 330 nautical miles across from northwest to northeast quadrant. This makes Irma a large hurricane, which in itself is dangerous regardless of Category 3 or 5. Why large hurricanes are dangerous?

Storm surge is the problem. Larger hurricanes produce higher storm surge. Let me repeat these hurricanes that were large. Hurricane Katrina in 2005. Katrina made landfall as Category 3 on Louisiana and Mississippi. It produced storm surge as high as 35 feet/10.7 meters! By comparison, Hurricane Camille made landfall in 1969 in the same area as a Category 5 hurricane, but produced storm surge of 25 feet/7.6 meters. Camille was smaller than Katrina. Hurricane Ike is another example of a large hurricane, which made landfall on Texas as a Category 2 hurricane in 2008. Ike produce storm surge as high as 25 feet/7.6 meters, which is highest outside of Mississippi! Hurricane Sandy made landfall as a Category 1 hurricane on New Jersey in 2012. It produced storm surge as high as 15 feet/4.6 meters.

Many areas in Florida will see storm surge as high as 15 feet/4.6 meters. This type of storm surge is dangerous. The land will be inundated with 3 feet/0.9 meters or greater. That amount of water rushing in is dangerous and will wash anyone away! Anyone who lives in storm surge areas need to evacuate! If you live in an area with no storm surge, you should hide, with the exception living in a mobile home. Case in point, too many people evacuated when Hurricane Rita came barreling towards Texas and Louisiana. Most people who evacuated did not need to evacuate. This came a month after Katrina ravaged Louisiana and Mississippi. Also, more people died while evacuating than in the actual hurricane. We are seeing that problem with Florida. People who really need to evacuate are people who live in storm surge prone areas.

Here is the forecast model of where Irma will go. This is the latest heat map from various forecast models and GFS ensemble track guidance for Irma. The GFS goes up to 10 days.

Most have Irma going northwards towards Florida. It could go west of Florida or over Miami area. Either way, it is going to be bad for Florida. Once Irma is inland, most forecast models have Irma over Tennessee and Kentucky. This could be an issue as hurricanes weaken and go inland, they can dump heavy rain, especially at night. The heavy rains often fall at night near the center of the warm core low. These thunderstorms converge closer to the center at night as the low pressure system is warm core and the ambient temperature is cooler. They are called core rain. Hurricane Harvey is a tragic example of core rains that led to massive flooding in Southeast Texas including Houston. The forecast model is five days, so anything can change now and tomorrow.

Here is the most recent intensity forecast. The intensity forecast model for Irma are all over the place.

Some keep Irma as a Category 3 hurricane, while others have Irma intensifying into Category 4. I would not be surprised if Irma intensifies to Category 4 or even 5 prior to landfall on Florida. Regardless, Irma is going to be a very dangerous hurricane. A weakening hurricane can be more dangerous because people think if it weakens, than they should be safe. Hurricanes that weaken are due to land interaction or eyewall replacement cycle. Those two can cause hurricanes to get larger. Also, once eyewall replacement cycle is done, the hurricane gets larger and stronger.

The wind radii gets larger in part due to land interaction and eyewall replacement cycle as Irma gets closer to Florida. This is why I keep saying larger hurricanes are dangerous regardless of Category 3 or 5. Here is a rainfall forecast model ending at September 16, 2017 at 7:00 PM. They are from GFS, EURO, Canadian, and Weather Prediction Center (WPC).

All are in agreement that Florida will get heavy rain from Irma. GFS and WPC have the heavy rain over the middle of Florida. EURO has the heavy rain over the western part of Florida. The Canadian has heavy rain over eastern part of Florida. The GFS has the heaviest amount of up to 35.2 inches/89.4 centimeters of rain. It is south of the Florida Keys. The EURO has 17.9 inches/45.5 centimeters of rain, which is also south of the Florida Keys. Most areas should see 8 to 12 inches/20.3 to 30.5 centimeters of rain from Irma.

Here is what I think will happen.
-Irma could affect Florida as early as tomorrow morning.
-Storm surge and high waves will be a problem on the coast.
-Strong winds and heavy rain will be the main problem inland.

The forecast models came from NCAR-Tropical Cyclone Guidance, National Hurricane Center, Weather.US, Weather Prediction Center (WPC), and NWS Key West. Special thanks to all of them.

It is going to be a long night and day for Florida. Let’s hope everyone is hunkered down in areas that have no storm surge. Anyone who is storm surge prone areas are away. This could be bad for Florida.


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