Hurricane Milton Has Deepened Rapidly into a Category Five Storm

What happened to Hurricane Milton yesterday is truly stunning.

Over one day, the strongest sustained winds in the storm strengthened from 90 to 180 mph.  It has subsequently weakened to "only" 165 mph.    Still a very strong category 5 storm.

The central pressure of the storm declined to 897 hPa (a unit of pressure) before increasing to 914 hPa.

The strongest Atlantic hurricane on record (Wilma) had a central pressure of 882 hPa..... not that different than Milton!

An infrared satellite image of Milton last night.   Not the beautifully forced eye...

a sign of a very strong storms

Milton revved up over a patch of warm water northwest of the Yucatan Peninsula.  We are talking about water in the upper 80s (F).  Fortunately, it is now moving over cooler water, which is contributing to a modest weakening.

Now let me show you some amazing simulations.   

Specifically, I will show you the surface winds from the high-resolution  NOAA/NWS HWRF model.   At 11 PM Monday, a very tight, ultra-intense storm of right off of the Yucatan. with maximum sustained winds at 174 mph.    Remember, gusts can be substantially higher, with some reaching over 200 mph!.  Wow.

Moving forward in time to 2 AM Thursday, the storm has expanded a bit, with maximum sustained winds of "only" 120 mph.  A category 4 storm.  

The approaching hurricane will push high waves on top of substantial storm surge, so coastal areas, particularly south of the low center, will be flooded. As shown in the forecast for late Wednesday, some of the waves could reach 30 ft.  And that could be on top of storm surge

 of 10-15 ft (see National Hurricane Center map below).   It is clear that the west coast of Florida from Tampa southward needs to be evacuated immediately.

North Carolina did not effectively warn and evacuate people for Helene and hundreds perished.   We can hope that Florida will be much more effective. 

Why Hurricane Track Forecasts are Much Better that Intensity Predictions

Tropical Storm Milton is now a hurricane heading for Florida's west coast.

As I will describe below, there is great confidence in the hurricane's future track but substantial uncertainty in its future strength.

Why the difference?  That is the topic of this blog.

Let me start by showing you the latest track forecast for this storm from a variety of forecast systems (see below).  All are taking the storm into the central portion of West Florida.

Not only are the track forecasts on the same page, but the verification of historical hurricane track predictions shows amazing skill and great improvement over time (see official National Hurricane Center forecast verification below). 

Around 1970, 72h-forecasts were typically off by 450 nautical miles.  Today the error is only about 75 nautical miles.   Very impressive.

So if you are anywhere on the central western side of Florida,  you better get prepared.  Now.

By what about the predicted intensity of this hurricane, which is now rapidly intensifying? 

There is some uncertainty in the future intensity, as shown by the predicted maximum wind speed (knots).   As shown below, some forecast systems intensify the storm into a very dangerous category 5 terror, with sustained winds over 140 kt, while others (blue line), keep Milton to a weaker, category 2.

Historically, skill improvement for intensity has been more modest than track (see below).

So why are track forecasts generally better than intensity forecasts?

To forecast the track of a hurricane, the critical issue is getting the winds around the storm correct.  Hurricanes are heavily steered by the larger scale wind currents and meteorologists have gotten very good in such predictions.

Why so good?   We have satellite data everywhere to start.   The U.S. has aircraft that fly out around the storm, dropping instrument packages, called dropsondes (see below), providing detailed, three-dimensional information around hurricanes.

With excellent computer models and extensive data, we can make skillful predictions of where storms are going.

But forecasting hurricane intensity is much, much harder.   Hurricanes are complex creatures, with intense bands of convection (thunderstorms) that play essential roles in providing heat and moisture to the developing systems (see far image of a hurricane below).

To simulate such rainbands requires very high-resolution models (very expensive) and getting essential physics correct, some of which we don't understand well.   For example, how breaking waves interact with winds to inject moisture into the storm.  

The complexity of the physics inside hurricanes makes the simulation of hurricane structure and intensity a very difficult problem.  We are making progress, but it is slow.

In any case, there is clearly a grave threat to Florida, with the landfall of Milton expected on Wednesday.  

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Announcement:  Free Public Lecture at Kane Hall on October 10:  Global Warming, the Jet Stream, and Cold Waves

All of you are invited to attend what should be an excellent public lecture by Professor Jonathan Martin on how global warming affects the jet stream and cold air outbreaks.

It will be a timely and interesting lecture accessible to non-meteorologists and given in honor of UW Professor Peter Hobbs.

The talk will be at 7 PM in Kane Hall room 210.

If you would like to go, please register online here:

Parking is available (at a modest cost) in the UW Central Garage, which is located directly under Kane Hall.  Or take the light rail (the UW stops are a 5-10-minute walk away).

The Seattle Times Needs To Use Weather Forecasts

 I walked outside on Friday morning around 7 AM to pick up my Seattle Times.  

What did I find?  A totally, sodden mess.   A hulk of wet pulp.  No plastic bag around it.

The same thing happened a few weeks ago.

The same thing happened several times last year.

Was this a surprise rain event?   

No.  Totally predictable.   

Typically, newspapers are delivered around 4-5 AM.    Here is the radar around 3 AM that morning.   Heavy precipitation was moving in.  One could have known this by using a free weather radar app.

The National Weather Service forecast had predicted the rain on Friday for DAYS (see forecast on Wednesday).

And the UW forecast model was essentially perfect the day before:

It is perhaps ironic that a newspaper that claims, with great authority, the ability to predict the climate decades ahead, can't use basic weather information in its distribution of newspapers.

As I will describe in detail in a future blog, the poor use of highly skillful weather forecasts is a major societal issue.

Not using forecasts properly led to the Maui wildfire disaster, severe wildfire death tolls in California, and most recently, the extraordinary loss of life in western North Carolina with Hurricane Helene.

Improved Chances for a Big Northwest Windstorm This Winter

We have gone several years since the last big windstorm from off the Pacific.

This year may be different.  This blog will tell you why.

The Chanukah Eve Storm of December 14, 2016

Major Northwest windstorms are associated with intense low-pressure centers reaching our coast and then moving to the northeast.   As illustrated below, these storms possess intense pressure differences around them, which produces strong winds.

Big Pacific cyclones hitting the Pacific Northwest are rare during strong El Nino and strong La Nina winters.

To illustrate this fact, the figure below shows you the sea surface temperature difference from normal in the central tropical Pacific, the key indicator of El Nino and La Nina, from 1860 through 2000.   Normal (or neutral years) are found from -0.5 to 0.5 C.  Moderate to strong El Ninos occur when temperatures are more than 1°C above normal.  Moderate to strong La Nina's when temperature is more than 1°C cooler than normal.  

The red dots show years with strong storms and high winds hitting our region.    Notice how they never occurred for strong El Ninos and La Nina.  Most windstorms occur in neutral to near neutral conditions (tropical Pacific sea surface temperatures are within 1°C of normal)

And now the key point.  The latest forecasts suggest we will be in neutral conditions or a  weak La Nina this year, a situation in which many big windstorms have occurred in our region.

Below is a graph showing a collection of predictions using different methods, some statistical, some using physical models.  Most are predicting neutral or weak La Nina conditions.   Good windstorm potential.

Why are neutral years better for strong low centers approaching our coast?

Major Pacific low centers/cyclones are closely associated with the jet stream.

During strong El Nino years, the jet tends to go south into California (see figure)

In contrast, for La Nina years, the jet stream tends to swing north of us, leaving our region in a northwesterly flow not favorable for strong windstorm development.  The last few winters have been dominated by El Nino conditions.

No guarantees, but I suspect we have a decent chance at a major blow this winter.

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Announcement:  Free Public Lecture at Kane Hall on October 10:  Global Warming, the Jet Stream, and Cold Waves

All of you are invited to attend what should be an excellent public lecture by Professor Jonathan Martin on how global warming affects the jet stream and cold air outbreaks.

It will be a timely and interesting lecture accessible to non-meteorologists and given in honor of UW Professor Peter Hobbs.

The talk will be at 7 PM in Kane Hall room 210.

If you would like to go, please register online here:

Parking is available (at a modest cost) in the UW Central Garage, which is located directly under Kane Hall.  Or take the light rail (the UW stops are a 5-10-minute walk away).

Why Such Catastrophic Flooding with Hurricane Helene?

 Hurricane Helene has brought terrible destruction to the southeast U.S., with the worst damage and loss of life in the higher terrain of western North Carolina.

The death toll is now well over 100 and the total damage is estimated to exceed 100 billion dollars.

As we will see, localized rainfall totals for the storm were extreme, with some locations receiving as much as 30 inches.

To understand what happened, first consider the terrain of the region (below).  You can clearly see the high terrain of the Appalachians over the northwest portion of the domain.

A map of rainfall totals for the event shows values reaching 15-25 inches on the eastern side of the Appalachians, where the hurricane pushed air against the terrain.

In fact, one location (Busick RAWS) had a 3-day total of 31.33 inches of rain, more than the annual total of many locations in the U.S.

The track of the hurricane was perfect for creating a very strong, moist, southeaserly flow that was forced up the eastern side of the barrier, dropping immense amounts of precipitation.

Northwesterners are very aware of the dramatic effects of geographic enhancement of precipitation:  as air rises on terrain it cools and is forced to give up its water vapor, which is converted into precipitation

Hurricane Helene at 5 AM PDT on Friday still had a very strong circulation (see pressure forecast for that time below).    Winds rotate counterclockwise around lows, so that the winds were from the southeast over western North Carolina

The hurricane entrained a plume of very moist air right into the eastern side of the Appalachians, something shown by a simulation of the winds around 5000 ft (850 hPa pressure) on Friday morning.  The purple color indicates the strongest winds...and the wind pennants show the direction.  The hurricane center was in the perfect location to push air into the North Carolina mountains.

The NOAA/NWS High-Resolution Rapid Refresh  (HRRR) model predicted the heavy precipitation in the right location  (see below).

Now the editorial portion of this blog.

The ability to forecast severe weather like this has gotten immensely better, with weather modeling technology enjoying profound improvement.   

But even with far better weather forecasts, there are still events with large death tolls, like this event and the Lahaina wildfire on Maui.    

Society must learn to better use advancing weather prediction to reduce the large death tolls in such events.