Hector Near Category 5 Strength; Still Expected to Pass South of Hawaii

August 6, 2018, 7:01 PM EDT

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Above: Infrared image of Hurricane Hector from the NOAA-20 polar orbiting satellite, taken at 6:27 am EDT August 6, 2018. At the time, Hector was a Category 4 storm with 145 mph winds. Image credit: NOAA.

Impressive Hurricane Hector is close to Category 5 status as it steams west at 15 mph across the Central Pacific towards Hawaii. Hector is expected to pass just over 100 miles to the south of the Big Island on Wednesday, and a Tropical Storm Watch was posted for that island at 5 pm EDT Monday. Hector may bring the Big Island tropical storm-force winds and a few heavy rain squalls. An Air Force hurricane hunter aircraft was in the hurricane Monday afternoon, and recorded surface winds near 155 mph--the border between Category 4 and Category 5 strength. Since Hector was far from Hawaii, the aircraft was only able to make one pass through the eye before heading back to Hawaii. Satellite imagery showed that Hector had a well-formed eye surrounded by an eyewall with very cold cloud tops, without much in the way of spiral bands. This type of structure makes Hector close to being an “annular” hurricane, an uncommon type of storm that tends to resist weakening.

Figure 1. Visible satellite image of Hector taken at noon EDT Monday, August 6, 2018. Image credit: NOAA/NWS/OPC.

Intensity forecast for Hector

The SHIPS model predicts that Hector will be over marginally warm waters of 26.5 - 27° (80 - 81°F) until it passes Hawaii on Wednesday. These temperatures are on the low end of what can sustain a major hurricane, and with Hector expected to move into a steadily drier environment, slow weakening can be expected, despite low wind shear of 5 – 10 knots. The NOAA jet was in the air on Monday afternoon flying a dropsonde mission, which should help the forecasts made during the 0Z Tuesday model cycle.

Hector forecast
Figure 2. Wind speed forecast for Hurricane Hector for 8 pm EDT Wednesday, August 8, 2018, made by the 6Z Monday run of the HWRF model. Tropical storm-force winds of 34 knots (39 mph, green colors) were predicted to brush the southern tip of the Big Island (top of image). Image credit: Levi Cowan, tropicaltidbits.com.

Track forecast for Hector

The 12Z Monday runs of our top models for tracking hurricanes, the European, UKMET, GFS, and HWRF models, all showed Hector passing about 100 – 150 miles south of the Big Island on Wednesday. The 5 pm EDT Monday Wind Speed Probability forecast from the Central Pacific Hurricane Center gave the southern tip of the Big Island a 34% chance of seeing tropical storm-force winds 39 mph of greater; Hector’s tropical storm-force winds extended up to 105 miles from the center at 5 pm EDT Monday. The 12Z Monday run of the HWRF model predicted that Hector’s heavy rains would remain south of the Big Island, with an inch or less of rain falling on the eastern sides of the Big Island and Maui. However, it would not be a surprise to see a band of heavy rain affect these islands on Wednesday, bringing isolated rainfall amounts of up to 4” that could cause localized flash flooding. For now, though, it appears that high surf will be the main threat Hector poses to Hawaii.

What would happen if Hector or some other tropical cyclone were to plow into the Big Island and its active Kilauea volcano? A recent weather.com article explores the hurricane vs. volcano intersection.

Hector likely to be extremely long-lived

The latest long-range forecasts from the 12Z Monday runs of the GFS and European models predict that Hector will stay far enough south during the coming week to avoid recurvature to the north and a death over the cold waters of the North Pacific. This track will likely allow Hector to cross the Date Line around August 14, when it would become the Northwest Pacific’s Typhoon Hector. The 12Z Monday run of the GFS model had Hector finally recurving to the north and dying on August 21, in the waters over 500 miles east of Japan. Hector became a tropical depression on July 31 and became a tropical storm on August 1, so it is possible the storm could be around more than 20 days, making it one of the longest-lived tropical cyclones and named storms on record.

The longest-lived tropical cyclone in world history was another Eastern Pacific hurricane that crossed the Date Line and became a typhoon: Hurricane John of 1994. John followed a 7,165-mile (13,280-km) path from the eastern Pacific to the western Pacific and back to the central Pacific, lasting 30.0 days as a tropical cyclone. John brought a few heavy rains showers and high surf to Hawaii, and caused $15 million in damage to U.S. military facilities on Johnston Island. Including John, there have been at least nineteen tropical cyclones that have lasted at least 20 days as a tropical depression or stronger.

Two more storms and an “Invest” in the Eastern Pacific: thanks, MJO!

In addition to Hector, there are two other named storms in the Eastern Pacific: Tropical Storm Ileana and Hurricane John. Ileana is the bigger danger, since it is closer to the coast. Its rainbands were affecting the coast of southwest Mexico on Monday afternoon, as seen on Acapulco radar. Ileana is not expected to intensify into a hurricane, but will be very close to the coast of Mexico through Tuesday morning, and tropical storm warnings were flying on Monday afternoon along a 400-mile stretch of the Mexican coast for the storm. The biggest threat from Ileana is heavy rains, though the forecasted rain amounts of 2 – 4”, with isolated amounts of 6”, should not cause widespread damaging flooding.

Tropical Storm John is the larger of the two storms, and is expected to intensify into a Category 3 hurricane by Wednesday. Upper level outflow from John is likely to cause high wind shear over Ileana, causing that storm to dissipate by Tuesday afternoon. John is headed to the northwest, parallel to the coast, and is far enough offshore so that it will likely not bring strong winds or heavy rains to the coast of Mexico.

In their 2 pm EDT Monday Tropical Weather Outlook, NHC gave yet another Eastern Pacific tropical disturbance, 94E, 2-day and 5-day odds of development of 70% and 80%, respectively. The system is located far out at sea, and is expected to take a west to west-northwest track towards Hawaii.

The high activity in the Eastern Pacific is due to several factors. High sea surface temperatures (SSTs) are one reason; SSTs beneath Ileana and John are near 86 - 88°F (30 - 31°C), which is about 1 - 2°F above average. The other key factor is the Madden-Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days. When the area of increased thunderstorms associated with the MJO is located in the Eastern Pacific, the associated rising air and low pressure can help spawn hurricanes, like is occurring now. According to weather.com, an enhanced phase of the MJO over the Pacific in late July 2017 helped trigger and outbreak of eight tropical cyclones in the Pacific, from southeast Asia to the Pacific Coast of Mexico. That was the most tropical cyclones to coexist in the northern Pacific Ocean since 1974.

Atlantic’s 97L no threat to land

In the Central Atlantic about 1100 miles west-southwest of the Azores, a non-tropical area of low pressure designated as 97L by the National Hurricane Center (NHC) was drifting slowly northeast on Monday afternoon. Satellite imagery showed that 97L had a well-defined surface circulation. The associated heavy thunderstorms had increased since Sunday, but was still quite limited. This low will be over marginal SSTs near 26 - 27° (79 - 81°F) and under light to moderate wind shear of 5 – 15 knots through Wednesday, which may allow it to organize into Tropical or Subtropical Storm Debby. If 97L does become Debby, this will be a short-lived storm, as a trough of low pressure passing to the north is expected to grab the system and accelerate it to the northeast over cold waters by Wednesday. In their 2 pm EDT Monday Tropical Weather Outlook, NHC gave 97L 2-day and 5-day odds of development of 30%.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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Dr. Jeff Masters

Dr. Jeff Masters co-founded Weather Underground in 1995 while working on his Ph.D. in air pollution meteorology at the University of Michigan. He worked for the NOAA Hurricane Hunters from 1986-1990 as a flight meteorologist.


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