Rare twin Category 1 hurricanes are nearing Hawaii as Hurricane Iselle
, with 85 mph winds, and Hurricane Julio
, with 75 mph winds, steam west-northwest towards the islands. Both hurricanes are expected to weaken to tropical storms before they affect Hawaii. Iselle is the bigger danger, as it is expected to make a direct hit on Thursday evening, while Julio's center is expected to pass about 100 miles to the northeast of the islands on Sunday. Satellite images
show that Iselle has weakened significantly over the past day. Though the hurricane still has a prominent eye, the eyewall's heavy thunderstorms are much reduced in intensity and areal coverage, due to wind shear and dry air. A new Air Force hurricane hunter aircraft is scheduled to be in the storm near 1 pm EDT Wednesday, and the NOAA jet will fly another dropsonde mission Wednesday evening. The outer spiral bands of Iselle were not yet visible on Hawaii radar
on Wednesday morning, but should come into view late Wednesday night.Figure 1.
Official forecast and uncertainty cones for Hurricane Iselle and Hurricane Julio, made at 11 am EDT Wednesday August 6, 2014. Image taken from our wundermap
with the Tropical layer turned on.Forecast for Iselle
Wind shear is expected
to stay moderate until Iselle reaches the islands Thursday evening. Ocean temperatures will remain a marginal 26°C, and the atmosphere surrounding the storm will steadily dry, resulting in continued weakening of Iselle. Just how weak the storm will be when it arrives in the islands Thursday afternoon and evening is a matter of considerable disagreement amount our top intensity models; the Wednesday morning runs of the LGEM, GFDL, and HWRF models predicted a strong tropical storm or weak Category 1 hurricane with 65 - 75 mph winds at 8 pm EDT Thursday, while the DSHIPS model predicted a much weaker system with 45 - 50 mph winds. Historically, only one tropical storm and no hurricanes approaching from the east have ever hit the islands, and this climatology would argue for a weaker Iselle on Thursday evening. The official CPHC forecast for a 60 - 65 mph tropical storm is reasonable, but Iselle could easily be a 50 - 55 mph storm Thursday evening. Regardless, the main threat from Iselle will be heavy rains leading to flash flooding and mudslides, and the storm will be capable of generating dangerous heavy rains when it reaches the islands. The Wednesday morning 12Z run of the GFDL model predicted that Iselle would dump widespread rains of 4 - 8" over the islands, with some regions seeing 8 - 16". Wind damage is also a concern from Iselle; the 5 pm EDT Wednesday Wind Probability Forecast
from Central Pacific Hurricane Center (CPHC) gave Hilo
on the Big Island a 72% chance of experiencing tropical storm-force winds of 39+ mph, and a 8% chance of hurricane-force winds. These odds were 30% and 2%, respectively, for Honolulu. High surf of 10 - 20' and higher will also pound the islands, causing erosion problems and coastal flooding.Figure 2.
Predicted rainfall along the track of Hurricane Iselle from the 12Z (8 am EDT) Wednesday August 6, 2014 run of the GFDL model. The model forecasts that Iselle will be a strong tropical storm with 60 - 65 mph winds when it hits the islands Thursday evening. Widespread rains of 4 - 8" are predicted over the islands, with some regions seeing 8 - 16". Image credit: NOAA/GFDL.Julio becomes a hurricane
Hawaii's other hurricane threat is Hurricane Julio
, which intensified to a Category 1 hurricane with 75 mph winds at 5 am EDT on Wednesday. Julio's ascension to hurricane status now gives the Eastern Pacific 10 named storms, 5 hurricanes, and 3 intense hurricanes so far in 2014. On average,
we expect to see just 6 named storms, 3 hurricanes, and 1 intense hurricane by August 6. Satellite loops
show that Julio is not very impressive yet, with only a modest area of heavy thunderstorms and no eye. The storm should be able to take advantage of light to moderate wind shear and marginally warm sea surface temperatures near 26°C to intensify 5 - 15 mph by Thursday. Higher wind shear and drier air should induce weakening beginning on Friday. The models have been increasingly enthusiastic about Julio taking a bend to the right in its track this weekend, putting the center of the storm about 100 miles northeast of the Hawaiian Islands on Sunday. On this path, Julio's core of heavy rains of 8 - 16" would miss the islands, and high surf would be the main impact of the storm. The edge of Julio's cone of uncertainly for Sunday still lies over the islands, so we cannot yet be confident of this track, but I am cautiously optimistic that Hawaii will avoid torrential rains from Julio falling upon soils already saturated by Iselle.Figure 3.
Tracks of all tropical cyclones (tropical depressions, tropical storms, and hurricanes) to pass within 100 miles of the Hawaiian Islands, 1949 - 2013. 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 one named storm approaching from the east has hit the islands since 1949, an unnamed 1958 tropical storm that 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
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. Tropical storms and hurricanes are rare in the Hawaiian Islands. 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 one tropical storm has hit the islands since 1949--an unnamed 1958 storm that hit the Big Island. 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.Figure 4.
Typhoon Halong as photographed and tweeted
by astronaut Reid Wiseman at 09 UTC August 6, 2014. At the time, Halong was a Category 2 storm with 100 mph winds. Typhoon Halong headed towards Japan
In the Western Pacific, Typhoon Halong
was a Category 2 storm with 100 mph winds at 8 am EDT Wednesday. Satellite loops
show that Halong has intensified since Tuesday, with concentric eyewalls and a prominent eye now visible. Halong is expected to affect Southern Japan as a Category 1 typhoon late this week. Bertha declared extratropical
In the Atlantic, Tropical Storm Bertha
has lost its tropical characteristics over the cold waters south of Canada, and NHC has issued its last advisory on the storm. There are no threat areas to discuss in the Atlantic, and none of the reliable models for predicting tropical cyclone genesis forecasts anything to develop in the next five days.Video 1.
The Discovery Channel's "Destroyed in Seconds" chronicles the devastating impact of 1992's Category 4 Hurricane Iniki on Kauai, Hawaii. Iniki was the strongest hurricane ever recorded to hit the Hawaiian Islands.