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Gonzalo the Atlantic's First Category 4 Hurricane Since 2011; Ana Takes Aim at Hawaii

By: Dr. Jeff Masters, 4:30 PM GMT on October 15, 2014

A Hurricane Watch is up for Bermuda as Powerful Category 4 Hurricane Gonzalo aims its 130 mph winds towards the island. Gonzalo is the Atlantic's first Category 4 hurricane since October 2, 2011, when Hurricane Ophelia reached 140 mph winds. Gonzalo walloped the northernmost Lesser Antilles Islands on Monday into Tuesday morning while rapidly intensifying from a tropical storm to a strong Category 1 hurricane. One person was killed on St. Maarten, and two others were missing--one in St. Martin and one in St. Barths, according to The Daily Herald. Twelve people were injured in Antigua.

Figure 1. People clear trees from the road in the aftermath of Hurricane Gonzalo on October 14, 2014 on the French Caribbean island of Saint Martin. Photo credit: STRINGER/AFP/Getty Images.

Forecast for Gonzalo
Data from an Air Force hurricane hunter mission and satellite loops on Wednesday morning showed that Gonzalo had a tiny 6-mile diameter inner eye, with a concentric 28-mile diameter outer eyewall forming. The inner eyewall will likely collapse by Wednesday evening and the outer eyewall will take over as the main eyewall in an eyewall replacement cycle. This process should halt intensification, and possibly reduce Gonzalo to Category 3 status by Wednesday evening. But with wind shear a light 5 - 10 knots and warm Sea Surface Temperatures (SSTs) near 29°C (84°F), Gonzalo should be able to stay a major hurricane into Thursday. If Gonzalo is able to complete its eyewall replacement cycle quickly, the hurricane could re-intensify some and be a Category 4 storm into Friday morning. It is more likely, though that Gonzalo reached its peak lifetime intensity at 11 am EDT Wednesday, as the official NHC forecast indicates. Water vapor satellite loops show some dry air getting wrapped into the storm, which will interfere with intensification. The 8 am Wednesday run of the SHIPS model predicted that by Friday morning, when Gonzalo will make its closest pass by Bermuda, wind shear would increase to 10 - 15 knots and SSTs would cool to 27°C (81°F.) This should discourage intensification, and may drive steady weakening. The models have come into better agreement on the track of Gonzalo, with our two top track models, the GFS and European, predicting in their 00Z Wednesday runs that the hurricane would pass 50 - 100 miles west of Bermuda between 8 am - 2 pm EDT Friday. At that time, hurricane-force winds should extend outwards about 35 - 45 miles from the center, and tropical storm force winds should extend 160 - 170 miles from the center. Thus, Bermuda is likely to see tropical storm-force winds, but not hurricane-force winds. In their 11 am EDT Wednesday Wind Probability Forecast, NHC gave Bermuda a 94% chance of experiencing tropical storm-force winds of 39+ mph, and a 37% chance of hurricane-force winds of 74+ mph. Keep in mind that the average error in a 2-day NHC Atlantic track forecast between 2008 - 2012 was 90 miles.

Gonzalo is also a threat to Newfoundland, Canada; the GFS and European models predicted in their 00Z Wednesday runs that Gonzalo would hit Newfoundland between 8 - 11 pm EDT Saturday. In their 11 am EDT Wednesday Wind Probability Forecast, NHC gave Cape Race, Newfoundland a 55% chance of experiencing tropical storm-force winds, and a 7% chance of hurricane-force winds.

Figure 2. MODIS satellite image of Tropical Storm Ana taken at approximately 7 pm EDT October 14, 2014. At the time, Ana had top winds of 65 mph. Image credit: NASA.

Tropical Storm Ana takes aim at Hawaii
Tropical Storm Ana was at the verge of hurricane status at 11 am EDT Wednesday, and represents a potential serious rain, wind, and storm surge threat to the Hawaiian Islands this weekend. Satellite loops show that Ana has a Central Dense Overcast (CDO) of high cirrus clouds, characteristic of an intensifying tropical storm close to reaching hurricane status. 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 Wednesday 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 26% chance that the storm would intensify by 35 mph into a Category 2 hurricane by Thursday morning. Our top two models for predicting hurricane tracks, the GFS and European models, both show Ana passing very close to the Big Island of Hawaii on Saturday morning, and it is possible that the island could experience tropical storm conditions for the second time this year. In their 11 am EDT Wednesday Wind Probability Forecast, Central Pacific Hurricane Center (CPHC) gave Kailua-Kona on the Big Island a 60% chance of experiencing tropical storm-force winds, and a 9% chance of hurricane-force winds. Honolulu was given a 44% chance of experiencing tropical storm-force winds, and a 4% chance of hurricane-force winds. The average error in a 3-day NHC Eastern Pacific track forecast between 2008 - 2012 was 117 miles, and the 2-day error was 82 miles. The Central Pacific Hurricane Center, which is making the forecasts for Ana, does not post its error numbers, but they are probably similar. Steering currents are expected to weaken as Ana approaches Hawaii, so the 3 - 5 forecast probably has higher errors than usual. Ana could very well miss making a direct hit on any of the Hawaiian Islands, passing 100 - 200 miles to the west, if the latest 00Z Wednesday forecast from the European model is correct.

Figure 3. Radar image from the South Hawaii radar at 7:49 am EDT August 8, 2014 of Tropical Storm Iselle near landfall on the Big Island. The radar beam is being intercepted by the high mountains of Hawaii, and cannot "see" to the northwest.

First Iselle and Julio for Hawaii, and now Ana?
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. Iselle killed one person and did $66 million in damage, according to Aon Benfield. Most of this damage ($53 million) came from the destruction of 60% of the state's papaya crop. Iselle was the strongest tropical cyclone on record to hit the Big Island; the island's other tropical storm, the unnamed 1958 storm, had sustained winds of 50 mph at landfall. (Older records from the Central Pacific Hurricane Center show at least one other tropical cyclone between 1900 - 1948 that probably made a direct hit on Hawaii: an August 19, 1938 storm that brought sustained winds of 60 mph to Oahu.)

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 Wednesday 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 Wednesday Tropical Weather Outlook, NHC gave 92E 2-day and 5-day odds of development of 40% and 60%, respectively. 92E is a threat to bring heavy rains to the Pacific coast of Mexico on Thursday and continuing into the weekend. As of Wednesday 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 Wednesday afternoon post.

Jeff Masters


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