A day spent grinding along the north coast of Cuba has slowed Hurricane Irma’s sustained wind speed to 120 mph, making it at least temporarily a Category 3 storm. At 11PM, the storm finally seems to be swinging to the northwest, the start of the long predicted turn that should take Irma up Florida’s Gulf Coast. As it crosses the gap between Cuba and Florida, the extremely warm water in the Straits of Florida could restore some of Irma’s previous speed, but it has lost some of it’s intense organization in the longer than expected trip over Cuba, and may not recover much, if any, of its earlier energy. Marathon and Vaca Key began reporting tropical storm force winds as of 9 PM EDT. The first hurricane force winds were detected in the Keys at 10 PM EDT.
The storm is moving very slowly at this point, between 7 and 9 mph, but it should pass over the Florida Keys some time in the early hours of Sunday morning, with the center of the storm currently predicted to cross near Cudjoe Key. The entire chain, from Key West down to at least Islamorado, can expect hurricane force winds. A dangerous, life threatening storm surge will affect all the Keys, as well as the coast.
From the Keys, the storm is expected to skirt the Everglades, and should be just off Naples by Sunday afternoon. The track slipped slightly west of earlier projections at 8PM EST, and west again at 11PM EST, but the storm is still expected to graze Sanibel and Captiva Islands. Landfall should be near Sarasota on Sunday evening. Irma will move into the Tampa / St. Petersburg area late on Sunday evening, still carrying winds of 120 mph. Irma is expected to move back over water, and make a second landfall south of Tallahassee on Monday. Over 18 million people are in the area that could be exposed to hurricane force winds.
Storm Surge Predictions
Coast |
Feet above Ground Level |
Cape Sable to Captiva |
10 to 15 |
Captiva to Ana Maria Island |
6 to 10 |
Ana Maria Island to Clearwater Beach, including Tampa Bay |
5 to 8 |
Card Sound Bridge through Cape Sable, including the Florida Keys |
5 to 10 |
North Miami Beach to Card Sound Bridge, including Biscayne Bay |
3 to 5 |
Clearwater Beach to Ochlockonee River |
4 to 6 |
Fernandina Beach to North Miami Beach |
2 to 4 |
Reminder: Storm surge is extremely dangerous. If you are in an area where storm surge is expected, seek shelter in a higher location away from the immediate coast.
Sunday, Sep 10, 2017 · 6:05:26 AM +00:00
·
Mark Sumner
And, dammit, Irma is back to a Category 4 storm with winds increasing to 130. It’s moving NW very slowly, at 6 mph. The increase in speed over the last hour suggests Irma may be reorganizing following its encounter with Cuba.
Waiting for more details.
Sunday, Sep 10, 2017 · 7:03:49 AM +00:00
·
Mark Sumner
As of 3 AM EST …
LOCATION...23.9N 81.3W
ABOUT 65 MI...105 KM SE OF KEY WEST FLORIDA
MAXIMUM SUSTAINED WINDS...130 MPH...210 KM/H
PRESENT MOVEMENT...NW OR 310 DEGREES AT 6 MPH...9 KM/H
MINIMUM CENTRAL PRESSURE...930 MB...27.46 INCHES
Hurricane Irma 11 PM EST Saturday 9 September 2017
ABOUT 30 MI...50 KM NNE OF VARADERO CUBA
ABOUT 90 MI...145 KM SE OF KEY WEST FLORIDA
MAXIMUM SUSTAINED WINDS...120 MPH...195 KM/H
PRESENT MOVEMENT...NW OR 305 DEGREES AT 6 MPH...9 KM/H
MINIMUM CENTRAL PRESSURE...933 MB...27.55 INCHES
Between the 8PM and 11PM reports, Irma finally made the move from west northwest, to plain old northwest. It’s starting to turn. The prolonged period of travel over Cuba not only weakened Irma a bit more than expected, it’s dropped the storm surge predictions in several areas—though by no means taken them down enough to eliminate danger.
From forecaster “Berg” at the National Hurricane Center:
Irma's nearly 24-hour traversal of the north coast of Cuba appears to have affected the hurricane's structure and intensity. An earlier NOAA Hurricane Hunter aircraft and a more recent Air Force reconnaissance flight both measured maximum flight-level winds near 105 kt and surface winds near 95 kt. The planes have reported a double eyewall structure, which has also been observed in WSR-88D Doppler radar data from Miami and Key West.
Earlier predictions had Irma returning to Category 4 strength and regaining 20 mph or more as it crossed extremely warm waters. That seems less likely now that the core of the storm is disorganized. Unless it can complete an eye wall replacement very quickly, 120 mph may represent Irma’s top speed from now until landfall.
The shift of Irma’s track from the East Coast to the Gulf Coast means that many of those now facing the storm were not expecting to face a direct hit up until the last day. It also means that many areas in Florida could be facing an extreme storm surge.
Looking at the predicted surge in more detail, here’s the very south end of Florida. In looking at the Keys, don’t interpret the blue and yellow areas of the keys as the only areas inundated. They’re all going completely under. Note that serious storm surge wraps around and into Homestead, which was devastated by Hurricane Andrew in in 1992. That disaster significantly altered the way America plans for and responds to hurricanes, but tonight the people of Homestead need to be prepared for both the winds and water that are coming their way.
Relatively low levels of inundation at Tampa Bay when compared to the incredible surge around Naples should not be taken to represent only slight danger or damage. Many areas around Tampa are predicted to experience surge over 5 feet — much more than necessary to send cars crashing down streets, leave boats many blocks from shore, shift buildings off their foundations, shatter windows, and represent an enormous danger to life. Much of the Gulf Coast represents a heavily built up area, with many communities directly on the water or connected to the Gulf through canals. The possibility of widespread damage is extremely serious. The density of construction in many of these areas is extremely high. The ability to withstand the expected surge, almost nonexistent.
The left side of this image shows a part of Marco Island south of Naples, with a population of 16,000 and an elevation of 0. The right side of the image shows the expected storm surge at Marco Island — greater than 9 feet above ground level for the entire island. There are a lot of communities like this on the Gulf side of Florida, places where canals sometimes take the place of streets. For these places, this is very near a worst case scenario.
Hope for a slow eyewall recovery and lots of wind shear to keep Irma on its heels as the storm moves toward Florida. This could reduce both wind speed and storm surge.