An Unmanned Saildrone Takes Weather Observations in the Center of a Hurricane

From the Cliff Mass Weather Blog

I have to admit that I was thrilled with the news.  

On Thursday, September 30, an autonomous (unmanned) sailboat, called a Saildrone, made it into the center of Hurricane Sam, a category four tropical cyclone, measuring extraordinary winds and seas.  

And it even sent back live video.

Saildrone 1045 Made It Into Hurricane Sam

The hurricane Saildrone project, a joint effort of NOAA and an innovative private firm (Saildrone, Inc), has the goal of collecting valuable surface observations within tropical cyclones.  Observations of the upper layers of the ocean and near-surface atmosphere are particularly valuable because they provide information regarding the critical transfer of energy and moisture from the warm tropical ocean into the lower atmosphere.

One of the missing pieces in understanding and forecasting tropical storms.

There is really only one way to get this information: by having observing assets at the ocean-atmosphere interface.   And no manned vehicle would dare enter such a severe environment.

On Thursday, Hurricane Sam was an impressive category 4 storm with the strongest sustained winds estimated at 125 knots (144 mph), with gusts to 150 knots (173 mph).  The central pressure was estimated to be 938 hPa.

Hurricane Sam on Thursday morning.   You can clearly see the eye.
The Saildrone (Hull 1045) appears to have entered the eyewall of Hurricane Sam, observing significant wave heights if up to 50 ft!  Take a look at a video clip of what it was like in the storm:
Wow.  Just amazing.

Richard Jenkins, the CEO of Saildrone, shared these observations from the boat that day.  Significant wave heights go to 14 meters (46 feet), with peak gusts reaching 114 knots (131 mph).

As described in several blogs during the past two years, I have been heavily involved with Saildrone, working with them to test the robustness and data quality of the platform.
Two years ago, we had a line of early generation Saildrones, with larger sails (see below).  Such a large sail turned out to be a real vulnerability with steep waves and strong winds.   

Last year, I served as the meteorologist for a test of new hurricane-ready Saildrones with shorter, stockier sails that are far less liable to sheared off or be damaged (check out the first picture above to compare).  Ironically, the historic Saildrone that entered hurricane SAM had a technical problem last year off the Northwest coast and struggled to reach the Washington Coast where it was retrieved.
As Richard Jenkins told me a few days ago… have to be ready for some losses and problems in the development of such a complex platform.
NOAA’s Pacific Marine Environmental Lab (PMEL) has been an active partner with Saildrone and is leading this year’s hurricane-PMEL experiment with five of the hurricane Saildrones in the Atlantic.  A really good national investment.
The hope is that a network of Saildrones will lay in wait across the Gulf of Mexico and tropical Atlantic each hurricane season, providing critical information within the dangerous environment in and near the eyewall of tropical storms.


The Second Edition of My Northwest Weather Book is Now Available!

My new book is greatly improved and expanded over the first edition, with new chapters on the meteorology of Northwest wildfires and the weather of British Columbia.  A completely revamped chapter on the effects of global warming on our region.  And it has been brought up to date with recent weather events and the imagery is improved greatly. 

Where can you get it?
Local bookstores, such as the University of Washington bookstore.  The UW Bookstore has just received several dozen copies.
Or secure a copy from the publisher:  UW Press.
Or Third Place Books in Lake Forest Park or Seattle.
And yes, there are online sellers like Amazon and Barnes and Noble.

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October 5, 2021 2:15 pm

What a magnificent surfboard!!!

Reply to  ChrisB
October 5, 2021 2:37 pm

So magnificent that i wish greta would have used it when she crossed the ocean.

Reply to  SxyxS
October 5, 2021 3:32 pm

Damm, SxyxS, you beet me to it ! :<))

Bryan A
Reply to  Hans
October 5, 2021 4:38 pm

So SAM was Estimated at Cat4 (113 – 136kn) but SAM was measured as a Cat3 @ 103kn
While the text of the report mentions measured gusts of 114kn actual recorded data only indicates max gust of 103kn

Reply to  Bryan A
October 5, 2021 6:09 pm

NOAA will need to figure out the adjustment schedule for such measurements, to assure they fit the political reality.

Bryan A
Reply to  Bryan A
October 5, 2021 8:34 pm

I also noted that th barometric pressure was ESTIMATED to be 938 (fairly low) while the new tool was only able to confirm a Measured pressure of 970 at the lowest. It seems that these storms are purposely being ESTIMATED to be far worse than they’re measured to be much like climate change models using ESTIMATED model output as actual measured data

D Boss
Reply to  Bryan A
October 6, 2021 4:56 am

the NHC has been over estimating strengths for about 5 years – one or two categories less actual wind speeds than they report. You can watch data streams in real time during these storms and debunk the official narratives.

Crying wolf is a dangerous game – if people stop listening to overblown warnings….

Shanghai Dan
Reply to  Bryan A
October 6, 2021 10:09 am

No, they’re not estimated wrong…

They are merely corrected.

Steve Z
Reply to  Bryan A
October 6, 2021 12:57 pm

It’s possible that the Saildrone never made it to the eye of the hurricane, or even the eyewall. If it made it into the eye, there would have been a sharp decrease in wind speed as the eye crossed over the drone, which was not observed in the data.

This means that the Saildrone may not have been in position to measure the highest wind speeds, or the lowest barometric pressure of the hurricane.

Many of the estimates of hurricane strength over the ocean (either minimum pressure or maximum wind speeds) come from measurements from manned planes that fly through hurricanes. For reasons of safety, these planes fly several thousand feet above the surface, and some of the wind speed and pressure data have to be extrapolated down to the surface.

There could be some errors in these measurements, since any air-speeds measured with a Pitot tube have to be corrected for air density, which depends on barometric pressure. The wind velocities have to be calculated by vector subtraction of the plane’s velocity (speed and direction) relative to the ground and its velocity relative to the air (which may be in error due to an error in barometric pressure), so this can lead to errors in wind speed measurements at altitude. Also, the extrapolation techniques for surface wind speeds may be different in hurricane conditions than during times of lighter winds.

October 5, 2021 2:16 pm

There is only one peak intensity. By measuring ever more instantaneous conditions within storms it becomes ever more likely we record that peak intensity. Storms are not getting stronger. We are just getting better at detecting peak strength.

To bed B
Reply to  Rob_Dawg
October 5, 2021 9:11 pm

I was thinking the same. Another barrage of “unprecedented” in the lame stream media.

October 5, 2021 2:21 pm

Interesting sensor platform.

J Mac
October 5, 2021 2:33 pm

Very interesting!

Rud Istvan
Reply to  J Mac
October 5, 2021 2:53 pm

Yup, went there and read up before commenting.

October 5, 2021 2:50 pm

The video is impressive and helps to reinforce in my mind how ridiculous is the concept of a 10-meter wind in the middle of the ocean in a strong hurricane. There is no way to measure the wind at a constant altitude above the ocean surface with the platform tipping and swaying and bobbing up and down with the gusty wind and waves, and even if there was, where do you determine the “surface level”? Is it from the base of the waves, the mid point of the average wave height, or from the top of each wave? And what effect does blowing ocean water/spray have on the wind instrumentation?

I’ve seen similar videos of the ocean surface in strong hurricanes taken by stationary weather buoys. Those buoys typically report winds much lower than the official advisory estimated “10-meter” one-minute wind average and peak gusts, even with eye wall passage. Granted, many of these buoys have wind measurements at 2-3 meters above a calm sea surface (no mast tipping), but extrapolating to a 10 meter height is quite difficult, if not impossible, and still subject to much uncertainty.

Last edited 20 days ago by oz4caster
Ron Long
Reply to  oz4caster
October 5, 2021 3:21 pm

Good point about the the standard 10-meter wind, and also mentioning the eyewall. I was in an air traffic control tower in Vietnam, in July, 1969, when a hurricane (typhoon) went over us. The wind gauge (anemometer) was about 25 meters above ground surface. The winds were gusting 15 or so knots, with episodic strong rain, then the wind speed started rising steadily. There was a plaque in the tower that said “Abandon Tower at Indicated wind speeds of 90 knots”, so started shut-down as the speed increased to 111 knots (127 mph) and blew steadily without gusting, a classic eyewall. After 15 minutes started to abate and get gusty. So, you need to be directly in the (inner) eyewall to get the max speeds, and it helps to be higher above the surface. Watching the video almost made me sea sick.

Reply to  oz4caster
October 5, 2021 4:24 pm

There is a way to do that and get fairly steady elevation control near the sea surface – see my other comment here in this thread

Reply to  oz4caster
October 5, 2021 6:12 pm

As I wrote above, NOAA will have to figure out the data adjustments.

spangled drongo
Reply to  oz4caster
October 5, 2021 9:12 pm

Yes, having been caught in the centre of a couple of cyclones about 400 miles off the east coast of Aus in similar wind strengths I found that the most difficult problem was negotiating the “waterfalls”.

Sailing under bare poles in those conditions is quite doable but you need the power to turn downwind quickly and surf the biggest of the waves as they arrive.

When you get above about 80 knots of wind usually the seas flatten and are less dangerous except if you are in a strong current running against the wind, which is often the case on a continental shelf, and that continues to make those waterfalls.

You sure don’t get much sleep.

Rud Istvan
October 5, 2021 2:52 pm

Really interesting platform. Saildrone founder spent a decade achieving the world land speed sail record before founding Saildrone. It is where he developed the sail foil shape and horizontal boom trim tab control. Uses the Iridium LEO comm network for data up and downloads. Solar feeding batteries for all the instrumentation and comms. Can stay at sea for a year without maintenance. And rugged enough to survive a Cat 4 eyewall with 140mph winds and 50 foot waves.
Good stuff.

Chris Hanley
October 5, 2021 3:02 pm

Inside Hurricane Sam:

Reply to  Chris Hanley
October 5, 2021 3:35 pm

Some images from the 1998 Sydney – Hobart yacht race.
A “perfect storm” in Bass Strait (off Sth East Australia)
Sadly, a number of fatalities.

Reply to  Chris Hanley
October 5, 2021 4:19 pm

Great video. I wouldn’t be too surprised if in the near future we might see adventure seeking tourists on a similar unsinkable vessel having a close encounter with a hurricane so they have bragging rights. You’d want to have a strong stomach or big buckets handy though.

There seems to be no limit to the risks people (even 90 year olds) are prepared to take for an adventure these days…just ask William Shatner! I’m sure Scott and Shakleton would never have imagined paying tourists regularly going to the Antarctic (even if only the more friendly bits).

Reply to  Alastair Brickell
October 5, 2021 4:37 pm

And do said “bragging rights” include a Darwin Award?

Reply to  Mr.
October 6, 2021 1:57 pm


However, it might eventually be possible to have a gimballed platform inside the passenger vessel so that you would remain upright (and hopefully unseasick) with a fantastic view. Could be quite an amazing ride and view! Especially as things are no doubt going to get “worse than we thought”.

October 5, 2021 3:59 pm

… significant wave heights if up to 50 ft!

I’m a landlubber if ever there was one however …

I remember standing on the top deck in the lee of the bridge, about thirty feet above
the water line, and looking up at the tops of the waves. As far as I could tell, it was normal weather on the North Atlantic.

Is there some other factor, besides just height, that makes waves dangerous or remarkable?

Reply to  commieBob
October 6, 2021 3:26 am

Yes, wavelength. Waves in the open ocen tend to be long. A 20 foot wave at sea is no big deal I’ve been in 50 footers, BUT a 20 foot wave in the Great Lakes is a BIG deal. In the Lakes the crests are close together and will beat the crap out of you.

Reply to  Yooper
October 6, 2021 4:32 am

That is more of a concern for small/short vessels, whose length is relatively small compared to the wavelength of the waves. For large oceangoing vessels, wave length is not as important as wave size and wind strength, for the reasons I give above in my response to CommieBob. Also, total wave height is not the only consideration – whether the waves are breaking or have steep wavefronts, which even in deep ocean waters can occur with hurricane force winds, also makes a large difference in the pounding a ship takes.

Reply to  commieBob
October 6, 2021 4:27 am

Large waves put tremendous stress on the hull of a ship, which acts like a beam, bending into a U shape as the bow is lifted by a wave front, or smashes into the wave front if it does not rise with the wave sufficiently. Multiply that by hundreds or thousands of cycles, and a ship’s hull can break due to cyclic stress.

The other danger of large waves is if a ship is unable to cross the waves perpendicularly, or at the preferred 45 degree angle. Combined with high wind speeds, and a ship with high sides (like a typical container ship) that acts like a sail, a ship can rather easily be put sideways to the waves, which is called “broaching”. A big enough wave against a broached ship can easily cause the ship to capsize, which usually sinks the ship and kills everyone aboard.

A broach can also result from a loss of ship’s power leaving it totally at the mercy of the wind and waves. A ship that takes a tremendous pounding from heavy seas is also more prone to suffering a loss of propulsion.

Finally, a continuous pounding of waves can cause a hatch failure up forward, which can quickly sink a ship due to flooding forward in heavy sea.

Tom in Florida
Reply to  Duane
October 6, 2021 4:45 am

As an embarked troop aboard an LPD in the South China Sea back in the late 70’s, we went through a typhoon. At one point the ship took several severe rolls causing a piece of equipment to break loose that killed a sailor. Storm waves are relentless and very dangerous.

Reply to  Duane
October 11, 2021 8:01 am

I disagree with your suiggestion of crossing the waves at a 45 degree angle. My training and subsequent experience is to have the seas either right astern at reduced speed or, if possible, at 15 to 20 degrees on the bow. This angle of 15 degrees is easiest on both vessel and crew. Once when I was an apprentice on a 12,000 ton cargo vessel with a full load of lead ingots I spent 4 days in the Great Australian Bight hove to at slow speed with very big seas and a wind of around 50 knots at 15 degrees and the vessel rode the waves pitching easily with mostly just spray on the foredeck. At 45 degrees the vessel would have been rolling violently and shipping heavy water on deck, not good for structure or crew.

October 5, 2021 4:21 pm

Actually, there IS and has been a manned platform that can travel into the center of a strong hurricane, with little to no risk to the platform or the people riding in it … as I can personally attest, having done so myself.

That would be a nuclear submarine coming to normal periscope depth and either raising a mast above the wave tops, or trailing a cable with a floating instrument pod to the surface.

My attack submarine back in the day actually penetrated to near the eyewall of a cat 4 typhoon in the western Pacific not too far from Japan, where it eventually came ashore. As nuclear submarines routinely do on patrol, we came to periscope depth several times to do what subs do but which I am not allowed to describe.

Based upon the roll angles we experienced, as previously correlated with known wave heights, our navigation officer estimated the wave heights at 50 feet or greater. We were rolling very hard, which was not a comfortable ride. It was great to finally end our little soirées
near the surface and head back down to our normal cruise depth!

As it happens, our nuclear attack submarines have better things to do than collect scientific data from the center of a hurricane or typhoon. But I suppose if a scientific research lab managed to convince the navy to deploy an instrument pack on an SSN that would be if value to the fleet, then it could be done and yield some interesting data.

Joe Crawford
Reply to  Duane
October 6, 2021 3:16 pm

“We were rolling very hard, which was not a comfortable ride.” Ahh, but as a friend once told me: “Some people pay Disney good money for a ride like that.” :<)

October 5, 2021 4:48 pm

Author says” A completely revamped chapter on the effects of global warming on our region.”

Are these “effects” what has happened in the past or imaginary things you think will happen based on guesses. You have no idea what will happen in the future.

Pat from kerbob
Reply to  mkelly
October 5, 2021 8:15 pm

Past events re-imagined.

From the Simpsons:

“Warning; may not have happened”!

Last edited 19 days ago by Pat from kerbob
Loren C. Wilson
October 5, 2021 5:34 pm

Cliff, there is a large discrepancy between the estimated barometric pressure in the eye of the storm (938 hPa) versus the measured pressure of 970 hPa. The barometric pressure is not usually measured any more, but comes from a correlation between wind speed and pressure. Does this mean the correlation is inaccurate or is there another reason?

H. D. Hoese
October 5, 2021 5:58 pm

Hey, real field work, not quite as good as being there, but close. Been in high enough seas to appreciate the video, never like that. Have talked to those who have and felt lucky to survive. Waves do block the wind some, not much help.

October 5, 2021 7:37 pm

Fascinating to look at the video and then go back and watch the imagery in “The Perfect Storm”. ILM worked hard to produce visuals that matched what interviews of many sailors produced. While the critics were scoffing at the images, a local Lt. Commander told me, “They nailed it!”

Reply to  wsbriggs
October 6, 2021 3:05 pm

How about some “real” storm footage:

Tony Taylor
October 5, 2021 8:04 pm

Nice looking toy.

Paul Johnson
October 5, 2021 9:43 pm

Rather than a network of Saildrones “laying in wait”, can they be made air-deployable and delivered in the direct path of storms?

Michael S. Kelly
October 5, 2021 11:47 pm

What a very cool concept. I applaud the people who made the Saildrone happen.

October 6, 2021 4:10 am

This is a cool idea, excellent use of technology. Why not use US Navy submarines to collect this data in the center of storms? Seems like an expenditure of a great deal of capital and effeort for something that can be done with existing technology and equipment.

Charles Fairbairn
October 6, 2021 4:14 am

I’m thrilled too with this.
Can these drones get the VERTICAL upwards velocity of the vapor movement in the dead center of the Eye? I’m dying to find that out as it would enable calculation of the rate of rise of the endemic enthalpy which drives the system and eventually results in the surrounding circular winds in the higher elevations.
The drop in barometric pressure is also very significant here as it reduces the Partial Pressure of water in the immediate water/atmosphere interface which in turn increases the rate of evaporation, already high at the sort of temperatures involved.

All fascinating stuff, particularly if we can get the actual figures to play with rather than sucking the ends of our pencils.

michael hart
October 6, 2021 1:48 pm

As with space research, sending humans may look good for TV but unmanned devices can do the same work at a tiny fraction of the cost.

Tom Schaefer
October 7, 2021 5:51 am

OT question for Cliff Mass re: northwest weather: It’s getting pretty close to economic SHTF and I’m thinking of buying a remote property near Craig Alaska, on Prince of Wales Island, to hide and fish until the worst is over. I’ve noticed its been raining there pretty much every day for a month. Is that normal and routine?

October 8, 2021 6:18 am

The raft looks like a good idea. Sampling the environment to get real-time data about what’s going on in a Hurricane is a great idea and will advance the knowledge of how they work considerably. Hopefully Greta will be able to man one of these devices to enjoy that environment herself! LOL! But …

“And no manned vehicle would dare enter such a severe environment.”

Really? Ask hundreds of Coasties, Squids, and Merchies about that. I have seen 40+ foot seas on a relatively small Coast Guard Cutter, 180 Foot seagoing buoy tender, in the Pacific in 1984. We were in those seas for about a week. It was a roller coaster ride on steroids!

I road out Hurricane Anita in the Gulf of Mexico in 1977 on a 210 foot cutter. We sailed near the eye wall but eventually we turned around – that was an experience in 30 foot seas – and sailed out. I know a lot of former shipmates that have also sailed into storms as bad or worse than anything ole Sam could spin up. While I don’t recommend anyone sail into any hurricane there are times when it happens, either by accident or on purpose.

You just can’t say things like that quote if you have no real experience as a mariner. Coasties go into storms regularly to save the knuckleheads that get caught in those storms. How bout the young man, an aviation rescue swimmer, that was dropped into the ocean from a CG Helo to save some folks on a sinking sailboat off of NC that got caught in some very rough seas. Did his job, then wound up spending the night in a small raft until the CG could get out to pick him up. The helo that dropped him was at the end of their fuel supply – at least the amount that would get them back to E-City, NC – and they couldn’t stay long enough to hoist him back aboard. The seas were running in the 40+ foot range and winds over 75+ knots. I’m sure that was a long night for him. A CG C-130 fixed wing A/C stayed overhead to make sure they could keep an eye on him until he could be rescued. This happened back in the mid-90s.

So unless you’ve sailed on something other than a Carnival Cruise ship, keep your comments about sailing into hurricanes to yourself! Underway is the only way! LOL!

Semper Paratus!

October 9, 2021 6:37 am

Great concept, but to really sample as hurricane it doesn’t have the speed nor maneuverability for the operators to position it with precision. I’m pretty certain that once it gets into gale force winds it becomes flotsam. At the mercy of the wind and waves.

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