West Coast Wind Blog: Hurricane Irma… a little diversion from west coast winds.

Strongest Atlantic Hurricane ever in recorded history? Updated Wed. Sept 6, 2017

by Mike Godsey, mike AT iwindsurf.com


Update: This first video is the eye of Irma with average winds of 185 mph Tuesday Morning.

Fox News has declared that Hurricane Irma is the strongest Atlantic hurricane in history while other meteorological sources say it is the 5th strongest.

What is clear is this Tuesday afternoon is that this hurricane has peak winds around 180 mph as  measured by Hurricane Hunter aircraft and a dropsonde into its eye found a pressure of 927 mb. and dropping. This places it well above the threshold for a Category 5 storm.

Weak wind shear aloft, very warm 85F water temperatures and increasing humidity are factors favoring intensification.

This animation show how one model, the ECMWF, projects the trajectory of Irma from today, Tuesday Sept 5, through next Tuesday. This ECMWF model animation is not optimized for hurricane forecasting but if you look at the optimized imagery in the second image you can see that there is a lot of agreement regarding Irma’s trajectory.

Notice that some of the forecasts have Irma passing right over the mountainous backbone of Cuba. While this would be devastating for Cuba the mountains would greatly weaken and disorganize the storm which would benefit the USA.

Posted in Cape Cod, Chesapeake Bay, Coastal Georgia, Coastal South Carolina, Columbia River Gorge, Connecticut, Delmarva, Los Angeles, Massachusetts North Coast, New Jersey, Outer Banks of North Carolina, Rhode Island, San Diego, San Francisco, SouthEastern North Carolina, Tidewater Virginia

2017 Eclipse Shows Meteorological Effects Along the Charleston, SC Coast.

By WeatherFlow meteorologist Shea Gibson

There is no doubt how cool the Eclipse 2017 was for folks that lined up in its path to see. I was one of the fortunate ones along coastal SC that was able to get a good view of it..and WOW! It was quite the experience!

I was at front Beach, Sullivan’s Island at Station 28.5 overlooking the ocean and paid very close attention to the wind and weather while there. We were at the “Egg Shell” home..also known as the “Hurricane Home”.

There are lots of great pictures of the full coverage, these being from my lovely wife Amanda. 🙂

One really unique thing I noticed (with assistance from watching fellow kiteboarders on the water) was how the wind steadily picked up as the sun became more and more shadowed. The speeds actually peaked right during the total shadowing phase of the sun. Afterwards, the winds steadily fell to very light speeds.

Here are the wind graphs from Datascope and iKitesurf to all 3 local beaches in the Charleston area that fell under the total darkness…being Isle of Palms, Sullivan’s Island and Isle of Palms. Notice that all the winds turned E/SE for the start through end of the phasing (started shadowing ~12:00pm with peak darkness at 2:45pm, then sun coming back out through 5pm).

The Folly Beach sensor is tricky because it had earlier T-storms that fizzled out, was on the very edge of the darkness line…and it also has a spire at the end of the pier which blocks winds from the SE, so you see a dip in the winds that is not actually present. So, ignoring the downward dip just before peak darkness, we can assume the average continued to inch up to the peak shadowing at 2:45pm. 

The other things noticed were thunderstorms lined up along the Sea Breeze front inland gave off quite a lightning show as the shadow grew over the area.

On the way to the beach late morning, I checked the clouding, which showed that typical bullish cumulonimbus structure (anvil shaped thunderheads) beginning to develop inland. However,  driving back over the Isle of Palms connector after the peak event, I noticed the cloud types had that purplish cumiliform tower-like structure, which generally signifies a nocturnal or nighttime convective pattern where a warm layer is trapped aloft. Basically, the sun being shadowed interrupted the (radiational) heating process and caused the atmosphere to sort of “switch” to a night time pattern.  Unfortunately, the Charleston radar was down so I downloaded Level II radar data from the Columbia, SC NEXRAD site to update here.
Quite a lightning show inland along the Sea Breeze front. Storms advanced towards the coast a bit earlier as the Sea Breeze retreated.

I also noticed that where I live following the eclipse into the late afternoon and evening, that the summer daytime Cicadas, the brush bugs known for their loud screeching sounds that drone on-and-on all day, were quiet. The evening crickets were quietly chirping and the birds were not out and about. This was very much a nocturnal shift in the wild life and it stayed that way through sunset. I also was told of farm animals going back to the barns and hunkering down as they would at night time as well. Pretty neat!

Here is a GREAT drone video from a friend of mine Michael Royal who panned around his home at Sullivan’s Island Station 28.5 during the eclipse.

All-in-all…this event did not disappoint on any level. Definitely worth seeing these full solar eclipses. And guess what? The next one will be in 2024 across the United States.

Shea Gibson
WeatherFlow Meteorologist/Wind Forecaster
Outreach & New Station Projects
SE Region/East Coast
Twitter: @WeatherFlowCHAS

Sources: WeatherFlow, Google Earth, NASA

Posted in Coastal South Carolina

West Coast Wind Blog: Tropical Storm Lidia makes for fast changing wind forecasts.

Wind patterns change fast for the Bay Area and Southern California.

by Mike Godsey, mike AT iwindsurf.com

As the remains of Tropical Storm Lidia moved from Baja waters to west of the Southern California Bight it shook up the wind patterns for both the S. F. Bay Area and Southern California making for fast changes in the forecast from the 7:30 AM forecast to the 11:30 forecast. This animation gives you an idea of some of the complexity of the situation.

Posted in Los Angeles, San Diego, San Francisco

Eclipse Weather

by Meteorologist, Kerry Challoner Anderson

After listening to my daughter’s description of her total eclipse experience I regret not making the effort to get myself in position to be in the path of totality.  Instead my experience included trying to prepare the midday update for Oregon and realizing that I could not see the where the extent of the low marine clouds because the visible satellite pictures need light and with the eclipse in full swing that was nowhere to be found.

I teach online classes and many of my students where in the path of totality. So I asked them to report on whether they noticed a change in the temperature and winds.   All reported a significant drop in temperature and winds.  Well the instruments report the same thing.  Here is a look at some select temperature and wind readings from stations in the path of totality.


Posted in Cape Cod, Coastal Georgia, Coastal South Carolina, Columbia River Gorge, Connecticut, Delmarva, Long Island/SE New York, Long Island/SE NY, Los Angeles, Massachusetts North Coast, New Jersey, Ontario- Simcoe, Ontario: Lake Erie, Ontario: Lake Ontario, San Francisco, SouthEastern North Carolina, Tidewater Virginia, Weather Blog

West Coast Wind Blog: Dome of upper high pressure brings heat and…

Calm Gorge Winds, Sparse Bay winds and Strong Southern California coast winds. And what about Hurricane Harvey?

by Mike Godsey

You have probably seen graphics like the one above from the Portland Press Herald during a heat wave. This is a very simplified depiction of the type of dome of upper high pressure that has been over the entire west coast the last couple of days.

So why does this dome bring on a heat wave, why does the heat linger and why does this have such a different impact on the winds in each region?

First let’s look at the big picture.

Here is the view of the northern hemisphere’s winds today at ≈ 18,000 ft. as depicted by the GFS model. Notice all the loops in the upper level winds. The southward dipping loops are called upper troughs while the northward loops are called upper ridges. These loops steer surface weather systems like the North Pacific High that create the wind at the surface. So a major key to forecasting surface winds is to track these upper events.

Now looking at the globe again find the USA’s west coast. Notice the upper ridge moving into Canada. Then notice  the upper trough out in the Pacific (and my note about Tuesday.) Most importantly notice the clockwise rotating mass of air at ≈ 18,000 ft. over the western USA. This is the heat producing dome of upper high pressure air.

Notice how the dome
seems cut off from the ribbon of upper level wind going around the globe. Once a high pressure is cut off like this it tends to linger since is not moved along the conveyer belt of wind that normally moves weather from W. to E across the USA.

Now look very carefully in the area of Texas and you can see the upper level winds over former Hurricane Harvey. Now can you figure out why the hurricane is modeled to linger over Texas for day with forecasts of up to 50 inches of rain?

Let’s take a closer look at the dome of high pressure. In this image you can see that the dome of high pressure is spinning clockwise over the western USA and covers the land from the Gorge to past Southern California.

The air within this spinning mass is subsiding or descending towards the surface.

As the air within the dome descends it heats up bringing on our heat wave as depicted in the next image. Why the spinning? Think back to the Coriolis effect you heard about between naps in high school.

All of this heating in the Columbia Basin, the Great Basin, the Central Valley and Willamette Valley causes the surface low pressure in those regions to expand. And with nearby mountains limiting the expansion means the low pressure has to bulge, following low elevation topography, towards the coast. As this happens it really changes location of the pressure gradients in the Gorge, the Bay Area and Southern California.

The easiest way to visualize the location of these valley low pressure features is to look at the isobars. Isobars are lines of indicating where the air pressure is equal. By looking at the isobars extending from an area of low pressure when can see where the pressure gradient is strongest since the closer the lines are to each other the stronger the change in pressure and the stronger the wind.

So looking at this last image notice how low pressure from the Willamette Valley has expanded out into the Pacific with the tightest spacing of isobars in the Stevenson and Rooster Rock area. Hence we have been seeing weak E. winds in that zone.

The looking at the Bay Area check out the Central Valley thermal low in green and notice how its isobars are bulging into the Bay Area. Typically in a heat wave the low pressure expand over Sherman Island and the East Bay spoiling the pressure gradient. And often it even expands over the coast so the AM and early afternoon winds are limp. But often in the late afternoon the low pressure retreats inland a bit so sites near the coast see late mild wind.

Lastly look at Southern California. Note how the isobars expand right to the coast. This means there is a strong pressure gradient over the coast so Southern California typically sees solid winds during a heat wave. However if it gets too hot the isobars you see along the coast may wobble over Belmont to Seal making for up and down winds.

So when does the heat wave end and normal wind patterns return? Go back to the image of the globe above. See the upper trough west of the USAat ≈ 18,000 ft.? That structure will begin to hit the west coast Tuesday. It will first impact the Gorge Tuesday morning and deepen the marine layer and indirectly jacking up the pressure gradient. Later afternoon to evening onTuesday the same thing happens in the Bay Area. So is a bit more to the east so the change to cooler weather and a deeper marine layer will probably be felt Wednesday.



Posted in Columbia River Gorge, Los Angeles, San Diego, San Francisco

West Coast Wind Blog: Modeled vertical wind profile of Hurricane Harvey

Below is an animation of the wind patterns of Hurricane Harvey on Friday Aug. 25 as modeled by the ECMWF.

Posted in Cape Cod

West Coast Wind Blog: Different images of eclipse

Here are some different views of the eclipse.

First are 3 animations I made from satellite imagery.

The second two photos show the eclipse’s light as it filters through leaves and illuminates asphalt driveway.


Mike Godsey


Posted in Los Angeles, San Diego, San Francisco

Eclipsing the Winds

by Meteorologist, Kerry Challoner Anderson

Today is the big day for astronomers and amateur observers.  Eyes will be turned toward the heavens to view the solar eclipse – that is if you have the right protective glasses. Fortunately the latest satellite shows that clouds will not spoil this event for much of the West.  


But while most of the focus is on viewing this phenomena  there are other ways to experience and observe it.  Here at Weatheflow we are all a bunch of science geeks so none of us are missing this event but our focus is not just of what the eclipse looks like.  We will also be watching to see how the change in solar radiation effects our temperatures and our winds.

The suns radiation is the heat source for our wind systems both large and small.  The unequal distribution and absorption of radiation creates warm and cool pools of air that drive our winds. As the moon passes between the earth and the sun, light will be blocked from hitting the earth’s surface.  In the path of totality there will be a  period of about 2 hours where the sun’s radiation will be diminished.  Just how much will that affects our temperature and winds is a subject that is up for debate.

Since eclipses are few and far between there are not many studies to draw from.  There are predictions that temperature could drop 10 degrees during totality.  

Weather data from the eclipse of 1900, which cut a path across the Southeastern United States was studied by  H Hein Clayton who determined that there were changes in temperature, wind speed and direction and hypothesized that a cold core cyclone had developed.  These finding were criticized and future studies have sought to prove/disprove his theory.

The latest and possible most comprehensive study of the effect of an eclipse came in March of 2015 when the United Kingdom lay just south of the path of a total eclipse. This event was studied to see if there were appreciable changes in the weather.  Professor Edward Hanna of the University of Sheffield coordinated the research.  His study revealed that on average the temperature dropped about 2 degrees Fahrenheit over 40 minutes. There was a detectable change in wind speeds but not enough that the average person would notice. Winds dropped by about 9 percent.  But there was no evidence of a change in wind direction which would disprove Clayton’s hypothesis that eclipses create cyclones.

What can we expect today?  While most of the West is clear the coast is contending with marine layer clouds. An upper level low has helped to stir up deep and intrusive marine clouds that have moved well inland for Northern and Southern California.  They will be slow to clear so head well away from the beaches if you want a good chance to view the event.

It will be hard to find a place where the winds will be strong enough to detect a notable change due to the eclipse.  With the marine layer in place and the early hour for the eclipse our sea breezes will not have had a chance to build. There will be few places where  you will experience a noticeable change due to the reduction in sunlight.  But if you do please send in your observations.  We will be here watching our graphs and will report what we see too.

Posted in Los Angeles, San Diego, San Francisco Tagged with:

West Coast Wind Blog: Decoding the Hatch and Swell Bluff Reports…

Your tool at times when the sensor is not accurate.

by Mike Godsey, mike AT iwindsurf.com

You have probably noticed that the Swell City sensor often reads inaccurately especially in the morning. This is because the only location for a sensor in the area is atop a 30 foot cliff on the waters edge near Swell City.

Because of this issue I try to send out a bluff report several times each morning to help you get a more accurate picture of the wind.


The one flaw of the bluff report is that it is describing visual things using a few words. One phrase that you will often see is “bands of lulls and gusts are passing through the Hatch and Swell zone making the sensor data suspect.”

Below is an image from today at 9AM showing what those bands look like. Clearly if you are on the water at the right time you will have great wind but as a lull passes through you may be slogging.


Posted in Columbia River Gorge

West Coast Wind Blog: We can forecast the eddies arrival and departure pretty good…

But often fail at the exact focus of it’s winds.

by Mike Godsey, MikeAT iwindsurf.com

Years ago when I first began forecasting when the models could barely resolve the entire Bay Area I and the NWS were oblivious of eddies off the Golden Gate. Sure ocean fishing party boats knew that sometime there were mysterious SW winds near the coast while northerly wind blew out at the ocean buoys. But know one was looking at how these eddies impacted Bay Area winds.

So these days we are pretty good at forecasting when an eddy is likely to spring up and produce SW winds inside the Bay. But we are still pretty poor at forecasting the exact sites  where the southerly wind will focus other than saying the wind focus will be mostly N. of the Bay Bridge. Why is that so hard? Well…..

First let’s look at the big picture. Way out in the pacific is the center of the North Pacific High and the winds spiraling clockwise from the high pressure.

But today, in response to upper level winds, the NPH has a extension or ridge leaning into the Pacific Northwest.

Why should bay kiters and windsurfer care about events off the Pacific Northwest? Because when the North Pacific High forms a ridge it’s NW coastal winds turn more NNW. Which means:

  1. Given the angle of the California coast it becomes harder for the ocean wind to curve into the Bay Area.
  2. And if conditions are right (or wrong if you sail the coast or most of the Peninsula) this NNW wind helps a counter-clockwise spinning eddy form west of the Bay Area like you see in this second animation.

In this second animation the wind focus looks easy to forecast. The SW flow should be strongest at Pt. Isabel, Berkeley and Sherman Island with weaker winds at Larkspur and Brickyards/Peacock Gap.

The problem is that this animation is just what one model suggests about the eddies location and shape. We typically look at about 5 models each day to get a rough handle on what the wind is likely to do that day. But when it comes to eddies the models can differ wildly.

This last animation show how today’s eddy (August 16, 2017) is modeled by the NAM3, ECMWF and GFS models. Notice that all 3 models depict an eddy off the Bay Area. But notice how differently they are in the shape and location of the eddy and the focus of the SW wind.

So how do we make a forecast from this mess? We look at the empirical data like the satellite imagery and the reports from all the ocean buoys and coastal sensors and see which model most closely reflects the reality.

From there we look at the focus of the pressure gradients to different parts of the Central Valley versus all the gaps in the coast range to see how the wind is likely to be funneled towards different sites.

So far so good! But the eddy often changes location and shape during the day. Which means blown forecasts.

Now you take a try at it. Here is the satellite imagery from about 8AM this morning. See the eddy just west of Pt. Reyes? Now which model from the animation above would you start your forecast from?

Posted in San Francisco