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Category 4 Gonzalo Closes in on Bermuda; Ana Disorganized, Still a Threat to Hawaii

By: Dr. Jeff Masters, 3:47 PM GMT on October 16, 2014

Hurricane Warnings are flying for Bermuda as one of the most powerful hurricanes ever to threaten the island, dangerous Category 4 Hurricane Gonzalo, aims its 145 mph winds towards Bermuda. After weakening briefly on Wednesday due to an eyewall replacement cycle, when the eye shrank to a minuscule 5 miles in diameter and the inner eyewall collapsed, Gonzalo successfully consolidated its new 20-mile diameter outer eyewall into an unbroken ring overnight. This allowed the hurricane to intensify from a Category 3 hurricane with 125 mph winds into a Category 4 hurricane with 145 mph winds overnight. That intensification process has now halted, as documented by three passes through the eye between 7 - 10:30 am EDT Thursday morning by a NOAA hurricane hunter aircraft. The plane found that the pressure had stabilized at 940 - 943 mb, a gap had opened in the southern eyewall, and a new concentric eyewall with a diameter of 40 miles had begun to form around an inner 17-mile diameter eyewall--all signs that intensification has halted. Wind shear is moderate, 10 - 15 knots, and Sea Surface Temperatures (SSTs) have cooled a bit, to 28.5°C (83°F). Infrared and visible satellite loops on Thursday morning showed an impressive well-organized major hurricane with plenty of intense heavy thunderstorms, excellent spiral banding, and solid upper-level outflow. This is not a hurricane that will weaken quickly.

Figure 1. MODIS satellite image of Hurricane Gonzalo taken at approximately 1:30 pm EDT October 16, 2014. At the time, Gonzalo had top winds of 145 mph. Image credit: NASA.

Forecast for Gonzalo
The 8 am Thursday run of the SHIPS model predicted that wind shear would remain a moderate 10 - 15 knots as Gonzalo approached Bermuda, and SSTs would cool to 27°C (81°F.) These conditions should discourage intensification, and may drive some modest weakening, but it is likely that Gonazalo will be a dangerous Category 3 or 4 storm with 120 - 135 mph winds at the time of its closest approach to Bermuda on Friday afternoon or evening. The latest suite of model runs has the hurricane passing less than 60 miles to the west of the island, which would put Bermuda in the strong right-front quadrant of the storm, potentially bringing them the strongest winds of Gonzalo's eastern eyewall. The models differ quite a bit on the forward speed on Gonzalo, with the 00Z Thursday run of the European model taking the hurricane just west of Bermuda near 10 pm AST Friday, and the GFS model predicting the closest pass at 4 pm AST Friday. Hurricane-force winds extend outwards about 45 miles from the center, and tropical storm force winds should extend 150 miles from the center. Thus, Bermuda is almost certain to see tropical storm-force winds, and pretty likely to see hurricane-force winds. In their 11 am EDT Thursday Wind Probability Forecast, NHC gave Bermuda a 99% chance of experiencing tropical storm-force winds of 39+ mph, and a 74% chance of hurricane-force winds of 74+ mph.

Gonzalo is also a threat to Newfoundland, Canada. Although the hurricane will likely be declared post-tropical on Saturday, it will still have Category 1 strength winds, and the GFS and European models predicted in their 00Z Thursday runs that Gonzalo would pass near Southeast Newfoundland between 2 am - 8 am EDT Sunday. In their 11 am EDT Thursday Wind Probability Forecast, NHC gave Cape Race, Newfoundland a 41% chance of experiencing tropical storm-force winds, and a 4% chance of hurricane-force winds.

Figure 2. Category 3 Hurricane Fabian bears down on Bermuda at 10:50 am EDT September 5, 2003. Image credit: NASA.

Bermuda's hurricane history
Ten major hurricanes of Category 3 or stronger intensity have tracked within 75 miles of Bermuda in records dating to 1899. Two of these were Category 4 storms, the most recent of which occurred on September 13, 1948. The most recent Category 3 was Hurricane Fabian of 2003, which made a direct hit on the island at Category 3 strength on September 5, 2003. According to the NHC final report, Fabian was the worst hurricane to hit Bermuda since 1926, doing $300 million in damage: "There was extensive damage to vegetation and considerable roof damage to houses in exposed locations. Some buildings had more severe damage, due to inherent structural weakness in some cases and possibly due to tornadoes (which were not confirmed) in others. There were huge (estimated 20 to 30 ft high) battering waves on the south shore of the island, with the reported storm surge estimated near 10 ft. Significant structural damage was inflicted as a result of wave action and/or surge." Fabian is the only hurricane to get its name retired exclusively because of its impact on the island of Bermuda.

Bermuda links
Current conditions
Bermuda radar
Port of Bermuda webcam
North Shore of Bermuda looking west webcam

Figure 2. MODIS satellite image of Tropical Storm Ana taken at approximately 7 pm EDT October 15, 2014. At the time, Ana had top winds of 70 mph. Image credit: NASA.

Weaker Tropical Storm Ana still a threat to Hawaii
Tropical Storm Ana was at the verge of hurricane status on Wednesday, with 70 mph winds, but increased wind shear overnight caused the storm to weaken and grow disorganized. Satellite loops on Thursday morning showed that Ana had recovered somewhat, with more heavy thunderstorms blossoming near its center, but mircrowave satellite images from the Navy Research Lab in Monterey show that Ana has nothing resembling an eyewall attempting to form, and it is unlikely that Ana can intensify into a hurricane on Thursday. Wind shear is light, 5 - 10 knots, and Sea Surface Temperatures (SSTs) are warm, 28°C (82°F), which is about 1°F above average. The 8 am EDT Thursday run of the SHIPS model predicted that wind shear would be light, 5 - 10 knots, and ocean temperature would be warm, 27.5 - 28°C (81 - 82°F) for the next three days along Ana's path, and gave a 19% chance that the storm would intensify by 35 mph into a Category 1 hurricane by Friday morning. It is more likely that Ana would become a hurricane on Friday evening, though, given the storm's disorganized condition on Thursday morning. Our top two models for predicting hurricane tracks, the GFS and European models, both showed in their 00Z Thursday runs Ana passing 100 - 200 miles west of the Big Island of Hawaii on Saturday morning. This is far enough away that the tall mountains of the island would likely be unable to disrupt the storm. In their 11 am EDT Thursday Wind Probability Forecast, Central Pacific Hurricane Center (CPHC) gave Kailua-Kona on the Big Island a 49% chance of experiencing tropical storm-force winds, and a 4% chance of hurricane-force winds. Honolulu was given a 46% chance of experiencing tropical storm-force winds, and a 3% chance of hurricane-force winds. With the model runs for Ana trending farther west of late, Kauai appears to the be the island most at risk of a direct hit, but the storm should be weakening by the time it reaches Kauai Sunday evening, due to higher wind shear.

Figure 2. Tracks of all tropical cyclones (tropical depressions, tropical storms, and hurricanes) to pass within 100 miles of the Hawaiian Islands, 1949 - 2014. Hurricanes approaching from the east typically fall apart before they reach Hawaii due to the cool waters and dry air that lie to the east of the islands. Only two named storms approaching from the east have hit the islands since 1949, an unnamed 1958 tropical storm and Tropical Storm Iselle of 2014, which hit the Big Island. Hurricanes approaching from the south represent the biggest danger to the islands, due to the warmer waters and more unstable air present to the south. The only two major hurricanes to have affected the islands since 1949, Hurricane Iniki of 1992 and Hurricane Dot of 1959, both came from the south. Image credit: NOAA/CSC.

Hawaii's hurricane history
Tropical storms and hurricanes are rare in the Hawaiian Islands, but 2014 is one of their most active years on record. Tropical Storm Iselle made a direct hit on August 8, Hurricane Julio passed just to the north of the islands a few days later, bringing high surf, and now Hurricane Ana threatens to cause more trouble. Since 1949, the Hawaiian Islands have received a direct hit from just two hurricanes--Dot in 1959, and Iniki in 1992. Both hit the island of Kauai. Only two tropical storms have hit the islands since 1949--an unnamed 1958 storm which hit the Big Island, and Tropical Storm Iselle, which made landfall along the southeast shore of Hawaii's Big Island on August 8, 2014 with 60 mph winds. On average, between four and five tropical cyclones are observed in the Central Pacific every year. This number has ranged from zero, most recently as 1979, to as many as eleven in 1992 and 1994. August is the peak month, followed by July, then September. A brief summary of the three most significant hurricanes to affect Hawaii in modern times:

September 1992: Hurricane Iniki was the strongest, deadliest, and most damaging hurricane to affect Hawaii since records began. It hit the island of Kauai as a Category 4 on September 11, killing six and causing $2 billion in damage.

November 1982: Hurricane Iwa was one of Hawaii's most damaging hurricanes. Although it was only a Category 1 storm, it passed just miles west of Kauai, moving at a speed of nearly 50 miles per hour (80 km/h). Iwa killed one person and did $250 million in damage, making it the second most damaging hurricane to ever hit Hawaii. All the islands reported some surf damage along their southwest facing shores, and wind damage was widespread on Kauai.

August 1959: Hurricane Dot entered the Central Pacific as a Category 4 hurricane just south of Hawaii, but weakened to a Category 1 storm before making landfall on Kauai. Dot brought sustained winds of 81 mph with gusts to 103 mph to Kilauea Light. Damage was in excess of $6 million. No Dot-related deaths were recorded.

Related posts
Climate Change May Increase the Number of Hawaiian Hurricanes, my August 6, 2014 post
Climatic Atlas of Tropical Cyclone Tracks over the Central North Pacific (2008)

Eastern Pacific tropical disturbance 92E a heavy rainfall threat to Mexico
In the Eastern Pacific, an broad area of disturbed weather (Invest 92E) was located a few hundred miles south of the Pacific coast of Mexico on Thursday morning, and was headed northwest at about 5 - 10 mph. With light wind shear, warm SSTs near 29.5°C 85°F), and a moist atmosphere, this disturbance is likely to develop into a tropical depression later this week. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave 92E 2-day and 5-day odds of development of 60% and 70%, respectively. 92E is a threat to bring heavy rains to the Pacific coast of Mexico on Friday and continuing into the weekend. As of Thursday morning, though, 92E's heavy rains remained offshore, as seen on satellite loops.

Moisture from 92E may move northwards across Mexico into the southern Gulf of Mexico's Bay of Campeche by early next week, contributing to the formation of a tropical or sub-tropical depression there by Wednesday, as predicted by the GFS and European models.

Hurricane expert Steve Gregory has more on the tropics in a Thursday post.

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.