Hurricane Gonzalo, east of the Bahamas, at 9:30 a.m. (NASA)

On Tuesday afternoon, Hurricane Gonzalo was upgraded to a category 3, and the second major hurricane of the 2014 season. By the next advisory, Gonzalo’s peak winds had intensified even further to 125 mph, making it the strongest Atlantic hurricane since Ophelia on October 2, 2011.

At 11 a.m. on Wednesday, Gonzalo was upgraded to a monster category 4 storm with 130 mph sustained winds, and slight intensification could still occur.  Prior to this, Ophelia in 2011 is the most recent category 4 storm in the Atlantic.

Models remain in agreement on a track that brings Gonzalo very close to Bermuda on Friday and then Newfoundland on Sunday. A hurricane watch is already in effect for Bermuda.

Probability of hurricane force winds over the next 5 days, beginning 8am Wednesday. (NOAA)
Probability of hurricane force winds over the next 5 days, beginning 8am Wednesday. (NOAA)

The forecast continues to look grim for Bermuda, which was just hit head-on by Tropical Storm Fay. Fay was almost a hurricane when it hit the island on Sunday.

Since 1851, Bermuda has had 47 hurricanes pass within 100 miles of the island.  Only 13 of them were major hurricanes, and 15 were during October.  Combining those criteria, a major hurricane passed near Bermuda in October just THREE times in the last 163 years.  The last major hurricane to visit Bermuda was Fabian in September 2003, and that was very destructive: An 11-foot storm surge, almost 80 percent power loss across the island, $300 million in damage, and four fatalities.


Tracks of the thirteen storms that passed within 100 miles of Bermuda as major hurricanes since 1851. (NOAA)

During Gonzalo’s formation and development, it was fortuitously under constant radar surveillance, first from Guadeloupe and then from Puerto Rico.  Frequent radar data of a storm make it easy to monitor the structure and position, especially when combined with aircraft reconnaissance.

But even in the absence of radar and aircraft coverage, valuable structural information is collected less frequently by satellites with instruments scanning at microwave wavelengths. There are several of these instruments in orbit, and at microwave wavelengths, they can “see” through the clouds and detect the underlying precipitation.


A portion of an eyewall replacement cycle is captured in this series of microwave images of Hurricane Gonzalo spanning nine hours. (NRLMRY)

Since exiting San Juan’s radar range, there have been a handful of helpful satellite overpasses that reveal what is known as an eyewall replacement cycle.  This is a normal intensification process that many tropical cyclones undergo.

During the cycle, the original eyewall slowly contracts, a new outer eyewall begins to take shape, the inner eyewall continues to contract and begins to weaken as the outer eyewall strengthens, and finally, the outer eyewall becomes the only one when the original inner one has completely dissipated.  This usually results in two changes, 1) the storm’s entire wind field expands in area, and 2) the intensity dips down a little during the structural transition but then can jump back up once the transition is complete.

In terms of accumulated cyclone energy (ACE), Gonzalo has already contributed more to the seasonal total than all other storms except for Edouard, but it has several days left to keep the tally going.  As of 8 a.m. Wednesday, 2014’s ACE has climbed to 53 percent of an average Atlantic hurricane season.