Hermine Hits Florida, Heads Towards Mid-Atlantic

Now a tropical storm, Hurricane Hermine hit the coast of Florida near St. Marks at approximately 1:30 am EDT Friday, September 2, 2016, as a Category 1 storm with sustained winds of 80 mph. Hermine was Florida’s first hurricane strike in nearly eleven years, since Hurricane Wilma of October 2005, and was the first hurricane to strike the U.S. since Hurricane Arthur hit North Carolina on July 3, 2014 as a Category 2 storm with 100 mph winds. One death is being blamed on Hermine so far, due to a falling tree in Marion County, about 150 miles southeast of where the center of the storm made landfall. As of 11 am EDT Friday, Hermine was located inland about 50 miles west-southwest of Savannah, GA, moving northeast at 18 mph. Hermine’s top sustained winds were down to 50 mph.


Figure 1. Radar image of Hurricane Hermine from the Tallahassee, Florida radar near the time of landfall, at 1:16 am EDT September 2, 2016.

Hermine brings a storm surge of 7.5’ to Cedar Key
Hermine brought a storm surge in excess of three feet to over 200 miles of the Florida Gulf Coast, from Apalachicola to Tampa Bay. The highest storm surge observed at any tide gage was 7.5’ at Cedar Key, Florida. The water level (storm tide, which includes storm surge and tide) rose to 7.64’ above mean sea level at 1:36 am EDT September 2; according to a Friday blog post by storm surge expert Dr. Hal Needham, this was the 5th highest water level since records began in 1880 at Cedar Key, and the highest in 23 years—since the Superstorm of March 1993. Hermine brought a maximum storm surge of approximately 4.2’ to Apalalchicola, 3.7’ at Tampa and 3.5’ at St. Petersburg. Late Friday morning, the storm surge from Hermine was still more than two feet high from Cedar Key to Tampa, and had built to one foot at Charleston, South Carolina.


Figure 2. Still frame from a September 1, 2016 Weather Channel Facebook video of the Cedar Key storm surge.


Figure 3. A street is blocked from debris washed up from the tidal surge of Hurricane Hermine Friday, Sept. 2, 2016, in Cedar Key, Florida. AP Photo/John Raoux.

High winds from Hermine cause widespread power outages
Hermine struck a relatively unpopulated stretch of the Florida coast with few observation sites. The strongest winds on land appear to have been at a Personal Weather Station (PWS) at Alligator Point, Florida in the northern eyewall of Hermine: sustained winds of 59 mph, gusting to 78 mph, at 10:25 pm EDT September 1, 2016. This station experienced the calm of the eye for over 50 minutes; it is interesting to see the upward spike in temperature of 3°F that occurred in the eye just after midnight. The highest winds at an offshore site were measured at Tyndall AFB Tower C, located about 20 miles south of Apalachicola, Florida: sustained winds of 61 mph, gusting to 79 mph, at 8:50 pm EDT. The anemometer on the tower is at an elevation of 35 meters, which is higher than the standard 10 meters used to reference surface winds, so these winds need to be scaled down to what they would be at a height of 10 meters for a valid comparison to other surface wind measurements. There were no measurements of hurricane-force surface winds during Hermine’s life, except by the Hurricane Hunters. Hermine’s strong winds brought down large numbers of trees, and about 253,000 customers were without power at the height of the storm on Friday morning in Florida. An additional 70,000 customers lost power in Georgia.


Figure 4. Observed rainfall for the 1-day period ending at 8 am EDT Friday, September 2, 2016. Hermine brought 24-hour rainfall amounts of 6+ inches to portions of northern Florida and Southern Georgia. The highest storm-total rainfall amounts over a 4-day period were near the Tampa Bay, Florida region; 18.89” fell at Baskin and 14.60” at Largo, just north of St. Petersburg. Hermine’s rains mostly missed Florida’s Lake Okeechobee region; on Thursday, the Army Corps of Engineers decided that the lake’s vulnerable dike is safe at the current water level, and elected not to increase the amount of polluted water released from the lake into its outflow canals that lead to the ocean. In May and June, large releases of Lake Okeechobee water to relieve pressure on the dike caused massive algae blooms and serious water quality issues along both coasts of Florida. Image credit: NWS/AHPS.

Extremely high moisture available to Hermine
Near record-warm ocean temperatures in the Gulf of Mexico are evaporating near-record amounts of water vapor into the atmosphere for Hermine to feed off of, and this moisture-laden air is surging northeastwards with Hermine. At 8 am EDT Friday, the upper-air balloon sounding at Charleston, South Carolina measured 2.60” of total precipitable water (TPW)—the amount of water that would result if one condensed all the water vapor in a column above and precipitated it out. This value ranked as the 9th highest TPW measurement of the 47,000+ balloon soundings taken at the site since 1948. On Thursday, Tampa, Florida measured its 2nd highest TPW measurement on record: 2.80”, during a special 2 pm EDT balloon sounding.

Correction: We reported earlier that an astonishing 3.25" of TPW was recorded this morning at the upper air sounding site at Nassua in the Bahamas--more than 5 standard deviations above normal. This reading was based on a daily summary prepared by the National Weather Service. However, Brian Brettschneider pointed out that this must be an error, since the site's previous highest TPW was only 2.8", and a cross check of sounding data from the University of Wyoming reveals that the TPW at Nassau this morning was actually 1.60".

The forecast for Hermine: Major storm impacts still to come
As of Friday morning, Tropical Storm Warnings extended up the Atlantic coast to Virginia, with Tropical Storm Watches now extending all the way to the Connecticut coast and all of Long Island, New York, including the New York metropolitan area. Hermine will continue rolling along or near the Southeast coast on Friday, gradually weakening before it emerges off North Carolina’s Outer Banks on Saturday. By that point, Hermine will have undergone at least a partial conversion into an extratropical (post-tropical storm), deriving energy from atmospheric dynamics rather than from the heat energy of the ocean. By later in the weekend, however, Hermine may again be resembling a tropical cyclone, as upper-level winds along its path weaken and upper-level ridging to its west, north, and east blocks its path.

Computer models are in agreement that Hermine will slow down Sunday into Monday in the Atlantic east of Delaware and south of Long Island, NY, roughly 150 to 200 miles offshore. The models suggest that Hermine may even carry out one or two tight cyclonic loops in this area. From Sunday morning through Wednesday morning, the official NHC forecast moves Hermine only about 200 miles to the northeast—an average motion of only 3 mph.


Figure 3. The official track forecast for Hurricane Hermine as of 11 pm EDT Thursday. Hermine’s dramatic slowdown is evident in the period from Sunday to Tuesday.

On Sunday, Hermine will be positioned near the north edge of the Gulf Stream, with SSTs of 27-28°C (81-82°F). These are more than 2°C above average for this time of year and more than adequate to support tropical development, regardless of whether Hermine is classified as a tropical or post-tropical storm by that point. As shown above, the 11 am EDT Friday outlook from NHC increases Hermine’s winds to the Category 1 threshold of 65 knots (75 mph) on Monday morning, with the center about 150 miles east of the Maryland shore. Hermine will likely weaken only gradually after that point, as it spins and crawls over the next several days. (Note that even if Hermine does become post-tropical, NHC will continue issuing advisories on Hermine as long as it remains a significant threat to land.)


Figure X. Sea surface temperatures for the last week of August 2016 (left) and departures from normal for the time of year (right), both in degrees C. Image credit: NOAA/NHC.


Torrential rains were pushing northward from Georgia to North Carolina on Friday morning, extending from the coast up to 200 miles inland. Flash flood watches are in effect from Georgia to Virginia along a belt northwest of tropical storm warnings. Rains of 4” - 8” totals will be widespread through this area, especially close to the coast. The dry weather in recent weeks will help tamp down the risk of large-scale flooding, although flash floods are still a risk whenever very heavy rain falls in a short amount of time. Rains of 1” - 5” and gusty winds will work their way up the Delaware and New Jersey coastlines from Saturday into Sunday, with the heaviest rains perhaps staying just offshore of the New York coast. There will likely be a sharp cutoff on the western side of the heaviest rain, so travelers and residents should be aware that a journey of just 50 miles or so toward or away from the coast could produce big changes in the weather you experience. Along with high surf, rip current risk will be high across many beaches for the next several days.

Major impacts possible on Mid-Atlantic and Northeast shoreline
Hermine is shaping up to be a prolonged, high-impact event for coastlines from Delaware to Massachusetts. As the center moves very slowly, Hermine will push vast amounts of water toward beaches, bays, and inlets. The winds and seas rotating around Hermine will have the greatest impact along the coast of central and northern New Jersey, Long Island, and Long Island Sound—the same areas hit hardest by Hurricane Sandy in 2012. Because Hermine is much weaker than Sandy and will not be plowing onshore as Sandy did, the highest water levels along the immediate coast are expected to stay well below the Sandy peaks, and coastal winds will be considerably less. However, because Hermine will be positioned offshore for several days, there will be a cumulative impact from relentless, battering waves and swells, and beach erosion could be severe. In addition, water will pile up in back bays over multiple tidal cycles, producing a prolonged rise in water levels and the potential for significant flooding in those areas.


Figure X. Although Tropical Storm Hermine is expected to remain off the mid-Atlantic coast, it will still generate large storm surge to its north and west. Guidance from the NOAA ESTOFS model indicates that the storm surge from Hermine could reach or exceed 4 - 5 feet on Sunday night along most of the New Jersey coast, the western Long Island coast, and western Long Island sound. Tides could either add or subtract as much as 2 - 3 feet to this total. This map is not an official forecast of storm surge or local impacts, since the timing and intensity of any storm surge is likely to evolve over the next several days. Image credit: NOAA Ocean Prediction Center.


Based on the GFS model forecast, NOAA’s ESTOFS storm surge model projects that a storm surge greater than 5 feet is possible along parts of the New Jersey coast at the western end of Long Island Sound late Sunday (see graphic). If this occurred at high tide, it could produce total water heights of more than 7 feet above sea level, which would be comparable to the expected surge impact of a Category 1 hurricane in the western sound, which adjoins low-lying LaGuardia International Airport.

The record surge from Sandy was in a class by itself, and Hermine will not cause the massive destruction of homes and businesses that Sandy did. However, in some locations, Hermine’s surge could be on par with levels observed in other noteworthy hurricanes and extratropical storms, including Hurricane Irene of 2011. This could lead to extensive disruption of everyday life in coastal areas of New Jersey and New York. The exact surge impact and the hardest-hit locations will depend on Hermine’s exact track and intensity Sunday and Monday, which are still too far away to pin down. It’s important to note that this surge-related flooding could easily occur even if the heaviest rains from Hermine remain just offshore, so residents may be at risk even where it hasn’t rained much. On Friday morning, the New York NWS cautioned that “Moderate to possibly major coastal flooding is probable” during high tide as early as midday Sunday, with storm surge of 3-5 feet atop high tide in western Long Island Sound and New York Harbor. The storm surge from Hurricane Irene in New York Harbor (omitting the tide) was 3.8 feet. Those living or traveling in flood-prone areas should keep abreast of NWS local statements on Hermine and heed any and all evacuation advice from local officials.

Weakening Gaston heads through the western Azores
A Tropical Storm Warning is up for the islands of the western and Central Azores as Tropical Storm Gaston speeds east-northeast at 18 mph through the western Azores. Down to just 70 mph winds as of 11 am EDT Friday, Gaston is expected to produce total rain accumulations of 1 to 3 inches over the western and central Azores through Saturday, when it is expected to become post-tropical. On Wednesday morning, Gaston peaked as an impressive Category 3 hurricane with 120 mph winds, becoming the season’s only major hurricane in the Atlantic thus far. The Azores only averages one hurricane strike per decade, and has already seen one this year: 2016’s first Atlantic storm, Hurricane Alex, which struck the island of Terceira in the central Azores on January 15 as a bizarrely out-of-season tropical storm in January. Alex did minimal damage and caused no direct deaths.


Figure X. Infrared satellite image of Hurricane Lester as of 1445Z (10:45 am EDT and 4:45 am HST) Friday, September 2, 2016.

Hurricane Watch continues for Hawaii ahead of Category 2 Lester
It’s quite rare to have two separate parts of the United States threatened by two hurricanes at the same time. So it was on Thursday night, with Hurricane Lester continuing to bear down on Hawaii. A hurricane watch is now in effect for the islands of Maui, Molokai, Lanai, Kahoolawe, and Oahu, including the Honolulu area. The Big Island has been dropped from this watch, since Lester is now too far north for its west-northwest track to affect the island.

As of 11 am EDT Friday (5:00 am HST), Lester was about 435 miles east of Hilo. Lester is now a Category 2 storm, with top sustained winds down to 110 mph as Lester travels over waters churned up by Hurricane Madeline just a couple of days ago. Computer models continue to agree on taking Lester along a west-northwest path that will parallel the Hawaiian island chain on Saturday, most likely as a Category 1 hurricane. The model guidance is now in fairly close and consistent agreement on a track just north of the islands, but the nearness of that track—perhaps within 100 miles—is enough to require continued vigilance. Huge surf can be expected regardless of the exact track. If Lester stays north as expected, the islands will be on its weaker left-hand side, reducing the chance of any major impact.

Invest 92L trying to organize in tropical Atlantic
Satellite images show that shower activity has increased in association with a large tropical wave located about 1000 miles east of the Lesser Antilles islands. Originally designated Invest 92L on Monday, this wave was no longer deemed worthy by NHC as an “Invest”, and they stopped issuing their suite of model forecasts for the system Tuesday through Thursday. The tropical wave was embedded in a major area of dust and dry air from the Sahara Desert, which was preventing development. However, on Friday morning, NHC resumed their interest in this system, and the latest SHIPS model forecast for 92L shows low wind shear and warm SSTs for the next five days, favorable for development, as it moves west at 10 - 15 mph. The latest 0Z Friday runs of our three top models for forecasting tropical cyclone genesis--the GFS, European and UKMET models—did not show development of the system over the next five days, and the large region of dry air that 92L is embedded in will keep any development slow. A strong and persistent ridge of high pressure should keep 92L on a fairly straightforward west to west-northwest path, and the storm will likely move through the Lesser Antilles Islands on Sunday, and be near Hispaniola on Monday or Tuesday. In their 8 am EDT Friday Tropical Weather Outlook, NHC kept their 2-day and 5-day development odds at 10% and 20%, respectively.

We’ll be back with our next update by midday Saturday.

Jeff Masters and Bob Henson