Tropical Depression Four-E: Could Hawaii See Impacts?

Jon Erdman
Published: July 8,2015

Highlights

• Tropical Depression Four-E formed Tuesday night and is currently located about 700 miles east of Hilo, Hawaii.
• Tropical Depression Four-E has a brief window of opportunity to strengthen into Tropical Storm Ela over the next day or so.
• This system is expected to move to the northwest over the next few days and pass north of Hawaii this weekend.

(MORE: Hurricane Season Outlook | Hurricane Central | Tropical Update)

Latest Status

Projected Path

So far, shower and thunderstorm activity has had difficulty persisting near the surface circulation due to south to southwesterly wind shear, displacing it from the center of circulation. This wind shear will only increase as the system moves northwestward, which means the window of opportunity for it to strengthen into a tropical storm is small.
If this system becomes a tropical storm – maximum sustained winds at least 39 mph – its name will be the next central Pacific name, Ela as it will form west of 140 degrees west longitude.

Enhanced Satellite

Hawaiian Concern?

Virtually every system approaching Hawaii from the east since 1950 tracking at least as far north as the latitude of the Big Island of Hawaii eventually weakened to a tropical storm or depression by the time it reached the islands.
We discussed the reasoning behind this in a piece written in August 2014.
Last August, Iselle became only the second tropical storm to landfall on the Big Island dating to 1950, after strengthening to a Category 4 hurricane.
Are we looking at another Iselle this time? In short, no.
First, an extension of upper-level low pressure currently swirling off the California coast will carve southwestward over the next several days, eventually taking it over Hawaii.
The winds aloft from this so-called "tropical upper-tropospheric trough," or TUTT, should have two impacts on the tropical system as it approaches:
1) Hostile wind shear – changing wind direction and speed with height – which tends to displace thunderstorms from the core of a tropical cyclone, limiting its strengthening potential.
2) Steering winds that would deflect the tropical system, assuming it becomes deep enough a circulation, to the north of the Hawaiian Islands.

Late-Week Steering Scenario

In fact, it's possible this wind shear could ultimately degrade the system so much it could be downgraded to a remnant low anytime over the next few days.
Interests in Hawaii should still continue to monitor the progress of this system, however.
At this time, here are the main impacts in the Hawaiian Islands this weekend from this system:

• High surf, particularly on the north shore of the islands
• Locally heavy rainfall from bands of rain and thundershowers on the south side of the circulation, not just in typical windward and mauka locations, but also in typically leeward locations.
• Lighter trade winds (Note the strongest winds with the system should remain north of the islands)

(FORECASTS: Honolulu | Hilo | Kona Coast | Maui)
Incidentally, hurricanes Julio and Ana also passed near the Hawaiian Islands in 2014. Ana was one of only four hurricanes since 1950 to pass within 150 nautical miles of Honolulu, dumping locally heavy rain and generating high surf.
This disturbance may not be the season's last to gain Hawaii's attention.
NOAA's 2015 central Pacific hurricane season outlook cited El Nino's tendency for reduced wind shear and more storm tracks coming from the eastern Pacific as reasons to expect an active season in the central Pacific Basin.
MORE: Hurricanes By the Numbers (PHOTOS)