Sea spray ‘static’ on radar is not a problem, NWS says

Question: I have been trying to find out why the weather radar at Ilio Point on Molokai has not been repaired in months. You will see the problem during weather reports on KHON, KGMB or KHNL. The weather reporters try to pass it off as "wind chop" or "false returns," but no one is doing anything to fix the problem. I called the National Weather Service, which said the radar belongs to the Federal Aviation Administration. I called the FAA and was told they would call me back, but no one did. As the situation stands, East Oahu is blocked out by this "wind chop," so you cannot see the weather, clouds, rain, etc. from Kailua all the way around the east end to about Manoa. Since this is an FAA radar, that means pilots use it to get weather updates. I am a commercial pilot and am concerned for all pilots who cannot see what is under this "wind chop." Why isn’t this radar being fixed?

Answer: The radar is not in need of any repair, and "false returns" do not block areas of East Oahu or hide anything, according to the National Weather Service.

In short, it says there is no cause for concern.

Raymond Tanabe, director of the NWS Pacific Region, explained that there are four weather radars in Hawaii — one on Kauai, one on Molokai and two on Hawaii island — all owned and maintained by the FAA but operated by NWS.

The "static" seen on the Molokai radar is not unique and appears on the Kauai and Hawaii island radars as well, he said.

It is caused by sea spray over the open ocean kicked up by strong wind.

Typically, there are stronger-than-normal trades during the spring, which is why "we’ve been seeing these broad and speckled areas on the radars over the past couple of months," Tanabe said. "There is nothing wrong or malfunctioning with the radars and nothing to repair."

He explained weather radars transmit a pulse of energy, then measure how much energy is reflected back when it hits particles in the atmosphere, such as raindrops.

"The radar is doing what it is supposed to do, which is locate water droplets in the atmosphere, and sea spray is a water droplet," Tanabe said. "Weather radars also locate other objects in the atmosphere, including bird migrations, insect swarms, dust clouds and smoke."

They do not necessarily differentiate between raindrops and insects — both are just particles or objects, he noted.

Over the past two years, NWS has installed new and upgraded radar equipment using dual-polarization technology, which allows meteorologists to really "see" into thunderstorms and other heavy rain clouds, Tanabe said.

"This technology helps us to issue flash flood warnings more accurately and with longer lead times, identify which clouds are likely to produce tornadoes, and determine whether snow or rain is falling," he said.

False Returns

National Weather Service meteorologists receive extensive training in interpreting radar images to help distinguish between returns caused by actual rain versus "false returns" caused by nonmeteorological objects, Tanabe said

"The presence of these returns from sea spray does not block areas of East Oahu or prevent folks from being able to ‘see what is under this wind chop,’" he said. "The sea spray returns do not hide anything either, and you will still see heavy showers if they are present (in addition to the sea spray)."

Meanwhile, Tanabe said weather service meteorologists in Hawaii conduct periodic training for various groups, including boaters, fishermen, pilots and volunteer weather spotters, on weather patterns in Hawaii and basic interpretation of radar data.

"We welcome the opportunity to provide similar training to all interested groups, he said.

If interested, he said to contact Christopher Brenchley, warning coordination meteorologist at the Weather Forecast Office in Honolulu, at christopher.brenchley@noaa.gov.

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