Changing of the Seasons

Below average temperatures in northern Utah have been few and far between the past few months, but the latter half of September has delivered the cool goods.  Since the 14th, we've only had three days with an above average maximum, and even most of the minima have been below average as well.  Simply splendid!

Source: National Weather Service

Leaves are starting to go now.  The cell-phone photo below doesn't do them justice as some there are some reds and yellows out there that are really starting to pop.  

With snow on the mountains, the feel has been more of October than September, but I'm not complainin'

Weather, Snow, and Ski Related Beers

I became a beer snob when I moved to Seattle in 1989 where there was already an flourishing microbrew scene.  Today, the term "craft beer" might be better since there are many excellent beers brewed by breweries of a variety of sizes. 

Some of these beers (and even some breweries) have weather, snow, and ski-related names.  Let's see if we can get a list together.  Here are a few of my favorite-named beers.  Most I've tried, but not all. 

Inversion IPA, Deschutes Brewing.  I typically drink IPAs in the summer, but this one takes the sting out of Utah's pollution during the winter.

Red Chair NWPA, Deschutes Brewing

Snow Cap, Pyramid.  This has long been one of my favorite winter ales, although it is not currently advertised on the Pyramid web site.  Hopefully it will arrive later this fall.

Edmund Fitzgerald Porter, Great Lakes Brewing.  I'm a big Porter fan during the cool season.  The Wreck of the Edmund Fitzgerald was a true weather catastrophe, made famous by the haunting song from Gordon Lightfoot.

Bombogenesis Double IPA, Chatham Brewing.  I haven't had this one yet, but may need to make a special trip downstate during my next visit to the hometown as this might be the best weather-named beer out there. 

Nor'eastah IPA, Chatham Brewing.  Another great weather-related name.  Designated driver definitely required for that trip.

Blueski Lager, Epic.  Epic brews several great beers without ski, snow, or weather-related themes.  I'm not much of a fan of lagers, but the ski theme gets a nod here.

Lake Effect, Proper Brewing.  A great name for this German-style ale, but sadly only 4.0% ABV.  Lake effect deserves so much more!

Mostly Cloudy, Long Trail Brewing. 

Sick Day, Long Trail Brewing.  None of you would ever know anything about sick days...

Runoff Red IPA, Odell.  Technically a hydrologic beer, but weather-driven.

Katabatic Brewing Co. Haven't been here yet, but this place gets a nod just for the name, with katabatic being a name for drainage flows and other buoyancy-driven downslope winds. 

Pray for Snow, 10 Barrel Brewing. 'Nuff said!

Add your favorites in the comments below.

Sunday Snowy Sunday

Yesterday was a remarkable September day, with record low maximum temperatures set at many northern Utah sites.

Source: National Weather Service

The recipe for a record low maximum temperature in northern Utah is to have not only a cold airmass, but also steady precipitation all day so that diurnal heating is limited.  Those ingredients were abundant yesterday.  Precipitation totals reported to the National Weather Service as of 8 PM last night included 1.46" in the upper Avenues, 1.34" in Cottonwood Heights, and 1.28" in East Mill Creek.  The Salt Lake City International Airport observed 0.89" of precipitation.  

I was shocked and surprised that we did not set a record low maximum at the airport, but the high reached 48ºF, whereas the record, set in 1934, is an incredible 41ºF.

In the mountains, it was Sunday Snowy Sunday.  I've seen reports from Alta of anywhere from 11 to 14 inches.  The Alta-Collins automated snow-depth sensor was at five inches Saturday at 3 PM and peaked at 20 inches at 8 PM Sunday.  You can call that 15" if you like.  Note that the depth sensor has been averaging around 4" all summer long, so the snow depth this morning probably sits at around 16 inches or so. 

And here's the spectacular view from Hidden Peak this morning. 

Doesn't that just warm the cockles of your heart?

Yup, this was simply an beautiful storm, if only it was late October.  Snow like this in September is a waste.  I'm sure a few people will be out there tempting fate today and getting turns, but the cover is poor and nearly all of this snow will turn to mud before we begin to build a seasonal snowpack.  Only the high-elevation shady areas have hope of survival and there, the snow should be nicely faceted when the next storm comes.  

Snow Update

In a tweet sent out at 8:21 AM, Alta Central reported 6 inches of snow overnight in the Town of Alta.

Albion Basin Summer Rd temporarily closed due to snow. Town of Alta 6 inches of snow and 28 degrees.

— Alta Central (@AltaCentral) September 24, 2017

Snowbird's Iron Blosam Cam shows a wintery scene.

More snow is coming today.  I suspect Alta will see the total reach about foot by the time things taper off this evening.

It's Cold, and It's Going to Snow More in the Mountains

Here are some numbers for the Salt Lake City Airport to put the cold of yesterday and today into perspective.

22 September
Observed Maximum Temperature: 53
Average Maximum Temperature: 76
Record Lowest Maximum Temperature: 52 (1895)

Observed Minimum Temperature: 41
Average Minimum Temperature: 50
Record Lowest Minimum Temperature: 29

23 September
Forecast Maximum Temperature: 57
Average Maximum Temperature: 76
Record Lowest Maximum Temperature: 47 (2000)

Observed Minimum Temperature: 40 (AM minimum, will likely stand for day)
Average minimum Temperature: 50
Record Lowest Minimum Temperature: 31

So, what has been most impressive from a cold perspective is yesterday's maximum, which was nearly a record low maximum for the day. Minimum temperatures are below average, but no where near records.

One of the great things about being a professor is having former students visit to take you out into the mountains.  I went out with a couple of my former graduate students today, hiking up to Maybird Lakes.  Yup, it was a cold start, but conditions were tolerable.  On the way up, there were even a few views.

I was surprised, given how cold it is, that the trees in the mid elevations hadn't turned more.  Next weekend will surely be better.

It didn't take long for the stratus to push in.  We got a brief view at the lakes, but things became socked in shortly thereafter.

I've been looking at the model forecasts for tonight and they have shifted toward even greater accumulations than indicated on Friday.  The 12Z NAM, for example, is putting out 1.25" of water and about 12" of snow at Alta from later today through late tomorrow.  The GFS is even more jacked, putting out 2.5" of water and 2 feet of snow, although that must be tempered by the fact that the GFS has a habit of going big at Alta more frequently than Mother Nature delivers.

I'm not sure what to expect.  The situation is one in which we're in the so-called "wrap around" precipitation region as the upper-level trough swings through.  This can be an area that does give decent snowfall, but it has to be in the right spot to give Alta a major dump.  At present (2:45 PM MDT), the National Weather Service is going for 2-4"tonight and 2-4" tomorrow at Alta, but I keep looking at the models and thinking we could do better.  Possibly much better.

This is a case of location, location, location and the possibility of a solid foot is there if things come together right.  Time will tell.  Really, snow now is not appreciated.  Early snow almost always turns into mud or, if it survives on shady high-elevation aspects, weak snow.  It would be much better if it held off for a few weeks.

The Last Hours of Summer

After a blistering hot warmest summer on record, the last few hours of summer giving us a blissful kiss of winter with a fresh coat of of snow in the mountains. 

Source: Snowbird

It's a bit difficult to gauge accumulations from what automated sensors are running right now in the Wasatch, but my guess based on the Alta-Collins total snow depth sensor is that they got about 3 inches or so overnight.  We'll see some additional snow showers today, although accumulations will perhaps be an angry inch. 

Tomorrow may provide a bit of a cold break, but given the instability, the possibility of snow showers remains.  Although accumulations will likely be limited, if I get out hiking, my plan will be to be ready for anything.  Even a brief period of snow squalls can be damn uncomfortable if you are traveling light. 

The big question mark for the weekend is what will happen as the trough swings Saturday night and Sunday.  The models are hinting that a more organized band of precipitation may develop during that period and affect the Wasatch.  See, for example, the NAM forecast below. 

Most members of our downscaled SREF generate about 0.2-0.5" of water during that period, which would probably equate to another 2-5" of snow.  There are, a couple members that are more enthused, including one ARW member that generates over 2 inches of water by Monday morning.  Ah, one can always find a solution to their liking in the ensembles, but recognize it is a low probability outcome. 

The bottom line for this weekend is keep an eye on forecasts and be prepared for cold unsettled weather if you are heading out and trying to do some hiking this weekend.  I'm already assuming that mountain biking is probably a nonstarter outside of the lowlands.

More September Snows?

Looks like a beautiful sunrise up in the Wasatch this morning, with a dusting of snow covering the mid and upper elevations.

Source: Snowbird

More September snow is in the way, although this is a fairly tricky forecast because the front that will drive our next round of precipitation is expected to slow and pivot as it moves into northwest Utah.

This results in challenges in both the timing and amount of precipitation expected.  This does, however, look to be an event that will produce some additional mid- and upper-elevation snowfall.

Most members of our downscaled SREF product are generating 0.4 to 0.8 inches of water equivalent for the event, with a mean of just over a half inch.  Note that there are contrasts in timing with some members getting things started Thursday afternoon, others later Thursday or Thursday night.

By and large, this looks to be a "dust on dirt" event, with perhaps 2-5 inches of snow for a storm total at Alta.  If that comes through, it would be our biggest storm of the season so far, good for tourism promotion, but otherwise a nuisance for hiking and other fall persuits.  There's a chance of more, but the odds of more than say 8" are low.  Bottom line: My skis remain in the rack.  

September Snows

Friday's storm brought a bit of the white stuff to the upper-elevations of the Wasatch Range, providing a boost to the morale of skiers and a nice contrast to the comparatively green grassy slopes remaining in early September.

By and large, the pattern over the next several days is more October like than September like.  First, we have a quick moving trough that gives us a brush-by late Monday and Tuesday.  This isn't a very deep trough and it's a close call on the placement of precipitation, but it could bring some light snow accumulations to the high elevations.

Then we have a deeper trough with the attendant cold front currently progged to push through Thursday morning.  This one is far enough out that we should be cautious about reading into details too much, but its a cold system for September (-4ºC at 700 mb/10,000 ft) and has some potential to give us a better coating than Friday's storm.

Then, the main upper-level trough and deep cold pocket swing through for next weekend.  Temperatures definitely more like mid October than mid September.

It's been a long time since we had a stretch of weather where things were biased on the cold side of average.  Enjoy!

Snowbird's Hidden Peak Cam Is Awesome

Snowbird has done a complete upgrade of their web site and perhaps their web cams because they seem so much better than they were a couple of months ago.  The Hidden Peak Cam is amazing.  You can't do it justice with a screengrab, but this morning's is below showing the dusting of snow, but also the abrupt transition of visibility when one gets to the top of what I think is the smoke layer that moved in with the latest cold surge.

Source: Snowbird

This is a meteorological preference, but I'd like to see a time stamp on these images, but I suspect they don't want to spoil them.  There is an indication of how old the images are on the web site.

BTW, it is a bit convoluted how to find the full size images on Snowbird's web site.  The direct link is here.  High frequency animations would also be appreciated (hint hint).

The Echo Chambers Are Giving Me a Headache

To all the pundits and activists out there acting like you are experts on extreme weather, hurricanes, and climate change, I have only one thing to say.

PUT A SOCK IN IT

This is a remarkably complex and difficult subject and you people are running around acting like you have it all figured out.  And there's plenty of room for a beatdown of people on both the right and left of this issue.  Gosh, the articles I am reading and discussions I am seeing are so absolutely horrific and they are setting weather and climate science back decades.

To those on the left who are conflating weather and climate, take a deep breath and let the scientists do their work and figure this out.  Don't lose sight of the fact that the IPCC issued a comprehensive report on extreme weather and climate change in 2012 entitled "Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation."  Here's what they had to say:

"The uncertainties in the historical tropical cyclone records, the incomplete understanding of the physical mechanisms linking tropical cyclone metrics to climate change, and the degree of tropical cyclone variability provide only low confidence for the attribution of any detectable changes in tropical cyclone activity to anthropogenic influences."

Plus.

"Attribution of single extreme events to anthropogenic climate change is challenging."

And this from the most recent IPCC assessment report, released in 2013.  See in particular the row for "Increases in intense tropical cyclone activity."

Source: IPCC AR5 Summary for Policy Makers

And for those of you on the right who have a smile on your face because of the above comments, wipe it off now.  Note that those statements pertain to cyclone activity.  We know that storm surge associated with tropical cyclones is worsening and will continue to worsen because of sea level rise.  And just because we can't say with confidence that global warming is having a detectable influence on tropical cyclones right now doesn't mean that (i) change isn't happening or (ii) that we won't see a clear trend in the future.  There are good reasons why we expect to see tropical cyclones become more intense and increase in destructive potential with global warming.  Finally, there are also good reasons to expect tropical cyclone precipitation rates to increase as well.  So quit hiding behind the natural variability and we've had storms like this before narrative as if that means we have nothing to worry about.

For those of you interested in a scientific summary of these issues, see Global Warming and Hurricanes on the GFDL web site.  

Ask and You Shall Receive

I know I should be talking about the changes underway in Utah's weather, but I'm still suffering from a case of Irma-itis, amongst other maladies.   So, instead, I want to address some questions being asked by our readers about Irma's track shift.



I am neither a theoretician, nor a hurricane expert, so let me just come out and say it.  I don't understand hurricane dynamics well enough to answer these questions in what I consider a satisfying way.

On the other hand, sometimes it's not worth thinking too much about these things.

The ability to for numerical weather prediction systems (hereafter computer models) to predict the shift in Irma's track reflects the culmination of decades of research not just in atmospheric sciences, but also computer science, remote sensing, and other fields.

A human, even with all the incredible observations we have today, could never have anticipated that shift with such precision days in advance without computer models.  The problem with the way that humans think is that we have to simplify and categorize things.  We need to take shortcuts.  We rely on analogs to past events.  We tend to think linearly, whereas the atmosphere is nonlinear and doesn't always behave in straightforward ways.

In contrast, computer models are not constrained by excessive simplifications, past analogs, or linear thinking. They solve a set of equations based on the conservation of momentum, conservation of mass, conservation of energy, and ideal gas law.  In other words, the laws of physics, and those laws are a beautiful thing.  

Of course, since we are doing this on a computer, some approximations are needed.  In addition, we are limited by computer time and this means we can't directly simulate every physical process.   Nevertheless, a model based on the laws of physics can do things we might not anticipate as humans.  It can predict events that have never happened before.  It does not rely on simplistic, linear thinking, like most humans do.

Our computer modeling capabilities have improved steadily and dramatically since they were first developed circa 1950.  First, we have made huge advances in how we create "initial conditions" for these models, through the development of improved observing systems (especially satellite based) and new techniques for bringing all of that data together into an analysis.  We have been able to add more detail to the simulation (called "resolution"), resulting in the improved simulation of physical processes that influence hurricane intensity and track.  We have developed ensemble modeling systems that produce many forecasts to try to account for the chaotic nature of the atmosphere so that we recognize the uncertainties in the forecast.

So, where does this leave us?  The bottom line is this.  Computer models today largely show us the way.  Yes, there are some phenomenon we struggle with mightily (snowfall in the Wasatch for example) and you can bet there will be a future hurricane that is not as well forecast as Harvey or Irma.  However, no human can integrate the laws of physics in their head.  Meteorologists aren't spending a lot of time on "why," but instead the "what", as in what are the possibilities, what are the hazards and impacts, what are the uncertainties.  Then there is the issue of communicating all of this complexity to the public and decision makers.  It's an end to end process that is imperfect, but the good news, it's getting better and I think there is every reason to be very optimistic that it will get even better in the future.  

More Not So Deep Thoughts on Irma Plus Utah Weather

I'm still feeling frisky this morning about several issues, so the not so deep thoughts continue.

Anderson Cooper is clueless
With Irma still threatening the southeast, I continue to scan the news coverage and find appalling statements.  Anderson Cooper has been especially effective at getting under the nerves of this meteorologist.

Last night, while interviewing the Mayor of Jacksonville, which was hit with severe flooding yesterday, he made the dumbfounding statement that "clearly people were caught off guard."  No Anderson, people in mandatory evacuation zones were not caught off guard. 

Social media and other communications challenges
It's been clear in the snippets that I've caught of Anderson that he really likes the caught off guard/surprise narrative.  This is very common amongst reporters because people love that angle.  It makes the story more interesting.

Anderson has frequently brought up the "westward shift" of Irma and how it surprised people.  As a meteorologist, I find this to be grating as well, but in contrast to saying people in mandatory evacuation zones were caught off guard, this has some merit, depending on where you get your weather information from.

Official forecasts from the National Hurricane Center were very cautious not to endorse a specific storm track up either the east or west coast of Florida at long lead time.  They also issued hurricane and storm surge warnings on both coasts, as well as the south coast and Key West.

However, many people do not see those forecasts.  Instead, they see national news, local news, and social media.  In that echo chamber, there is a tendency to gravitate toward especially extreme model forecasts and clusters of model ensembles that do not fully account for uncertainty.

Also an issue are misinterpretations of the NHC "cone of uncertainty."  That graphic is not intuitive for the general public, and needs improvement, but even some broadcast meteorologists don't understand it.

Let me show and example of how this effects the information that people receive.  Below and at left is a summary of the Key Messages for Hurricane Irma issued about 3.5 days prior to the landfall of Irma on Marcos Island.  The cone of uncertainty, which encapsulates the entire Florida peninsula and offshore waters.  The National Hurricane Center simply says that there's a treat of hurricane impacts over the weekend and early next week, with a likelihood of hurricane watches being issued on Thursday.

The right hand side provides an example of what people are seeing on social media, which says very strongly that Irma will hit Miami at Cat 4 or 5 on Sunday.  At that time, one could find model forecasts calling for that track and intensity, and advising people to leave was warranted, but the tweet suggests much greater confidence than evident in National Hurricane Center forecasts.

Traditional and social media today provides a firehose of content that is unfiltered and often without context.  At one time, it was difficult to see the forest through the trees.  Today, it is difficult to see the information through the misinformation.  Note that not all misinformation is malicious.  Sometimes it simply doesn't provide the necessary broader perspective.

This is why, in the case of tropical storms and hurricanes, I strongly urge people to monitor forecasts from the National Hurricane Center and local National Weather Service Offices.  While no forecast is perfect, these are the most reliable available.  The National Hurricane Center, in particular, has a remarkable team of scientists, with strong ties to the research and emergency management communities.  Finally, heed the recommendation of local officials.

HERE IT COMES UTAH!
OK, now that I've warned you about misinformation, let me provide a snippet from the latest forecast.  A bonafide midlatitude trough is expected to move over the Great Basin later this week.  Oh, it is a thing of beauty.

And here's the summary from the National Weather Service [note to my friends their, you forgot your logo :-)]

Source: NWS

I'm not counting the minutes.  I'm counting the seconds.

Not So Deep Thoughts on Irma

Hurricane Irma made two landfalls in Florida yesterday, one in the Keys, the other near Marcos Island on the southwest coast.  The low center subsequently tracked through west Florida and as of 8 AM EDT (6 AM MDT) was near the Florida coast west of Gainesville. 

Source: National Hurricane Center

Impacts cover the entire Florida Peninsula and Keys.  Although "worst case" scenarios did not play out for some, others are suffering severely.  Do not fixate on the news coverage, which shows a small microcosm of storm damage.  Everglades City, for example, wasn't even mentioned in the coverage I viewed yesterday, but reports heavy damage this morning.  Jacksonville is currently experiencing river and storm surge flooding.  News reports suggest almost 6 million people are without power.  Florida took a serious blow along nearly its entirely coastline and interior and it will take some time until we know the scope of it.  Recovery will take much longer.  

News Coverage

If you want to see a race to the bottom, just follow the news coverage of Irma, which has been like a David Letterman stupid human tricks skit.  How many people do we need to see attempting to report in eyewall rain and winds who just a couple of days previously chastised locals who elected not to evacuate and ride out the storm?  I know the first rule in news is "if it bleeds, it ledes," but imagine instead coverage that provides detailed information concerning storm details, winds, surge, and the like.  Something people could actually use.  Even The Weather Channel spent far to much time showing their people in the field and far too little providing information that might be of value to people.  Such a shame.

Official Forecasts

In my view, computer model and official forecasts of Irma's track and intensity from the National Hurricane Center were impressive.  @WxBDM tweeted this marvelous map yesterday showing the National Hurricane Center forecast uncertainty cones from Irma's inception to Florida landfall.  That cone represents the area in which there is a 2/3 chance that Irma will track.  Irma has always been inside that cone, and I believe that includes it's track through its current position in northern Florida.  

Source: https://twitter.com/WxBDM/status/906939915363131397

Intensity forecasts were also quite good, although perhaps made easier by the fact that Irma had the peddle to the metal for much of it's lifetime.  I read a majority of the discussions and forecast advisories issued by the National Hurricane Center with great interest and detail given my Mom's residence in central Florida and I didn't see anything in Irma's subsequent behavior that was not anticipated by the forecasters.  

This is not to say that the forecasts were perfect.  Track uncertainty was even larger north of Florida.  Specificity on wind, surge, and other impacts had shortcomings, although those in part reflect the state of the science.  We now we need to continue to advance the science and improve future forecasts to improve better decision making, but in the context of historical forecasts, Irma's represent a significant achievement. 

Traditional and Social Media

What one "sees" and the impressions one gets today are strongly shaped by both traditional and social media and represents a blessing and a curse.  I can't emphasize enough the importance of tuning out all that chatter and focusing on National Weather Service forecasts and the recommendations of local officials during hazardous weather.  While not perfect, those forecasts and recommendations are the most reliable, don't cherry pick one possible outcome or track unless justified, and offer you the opportunity of taking the best action possible.  

Thoughts on Today, 9/11

Sixteen years ago today, terrorists inflicted a horrific attack on our nation.  In the wake of that attack, first responders and many other heroes answered the call to duty, in some cases giving their lives or sacrificing their long-term health to help others.  Let us remember their sacrifices, and that the call to duty is being answered by many in Florida and the broader southeast US during Irma.  

"THIS IS AS REAL AS IT GETS"

Sobering words from the National Weather Service Key West Forecast Office in a tweet issued yesterday (Friday) afternoon.

NOTE: Tweet issued Friday with info as of 5 PM EDT.  Access the latest forecasts at http://www.nhc.noaa.gov/

That office is in a heavily fortified building designed to survive a hurricane.  I found it quite emotional watching a video late yesterday of them closing the storm shutters in preparation for Irma.
As I write this Saturday morning, Irma is sliding along the north coast and islands of Cuba.  Maximum sustained winds have dropped to 130 mph as it has been weakened some during interaction with Cuba.

Nevertheless, Irma remains a very large, powerful, and dangerous hurricane, and the National Hurricane Center anticipates restrengthening.

Irma will make landfall in Florida, but where will depend on the track.  The so-called "cone of uncertainty" contains the likely path of the low center, and covers most of the peninsula and immediate offshore waters over the Gulf of Mexico.

Wind and storm surge impacts will depend critically on the track, and making this forecast especially difficult is the fact that the storm will track along the Gulf coast.

Let's hope for the best.

Confessions of an Ivory Tower Meteorologist

Not so random thoughts on this Thursday.

Confessions of an Ivory Tower Meteorologist
I have something that I need to get off my chest.  Something that bothers me deeply. 

I get excited about extreme weather. 

I can barely sleep during weather events like Harvey and Irma, and I'm not even all that interested in tropical meteorology. 

I feel guilty about this.  After all, these storms are horrific, taking lives and destroying communities.

However, I also feel terror and nausea looking at both forecasts and the aftermath of these events.  It's a weird mélange of feelings. 

Meteorologists Are People Too
The National Hurricane Center is located in Miami.  Our nation is fortunate to have such a dedicated men and women working 24/7 to monitor and forecast tropical storms such as Irma.  Keep in mind that these meteorologists, their families, and their homes are also in the crossfire of Irma. 

Utah Alums Contribute to the Effort
I've been following the activities of an esteemed University of Utah alum and one of our current graduate students who are collecting critical data on Irma on one of the Hurricane Hunter aircraft.  Talk about living the dream! 

So Much Extreme Weather, So Little Time
One of the perks of my job is that I get to spend a lot of time looking at the weather.  A lot.  Your worst weather nightmare is my dream job. 

My preference is winter storms, but I am a weather omnivore.  I will consume whatever is available. 

Over the past two weeks, I've had a diet of all-time record heat, western wildfires and smoke, Harvey's record rainfall and flooding, and now one of the most intense Atlantic hurricanes on record.  Digging into these events challenges my knowledge and provides great teaching moments, but I can barely keep up. 

Mother Nature had better calm down soon.  I've been overeating and am starting to get fat. 

Back to work....

Irma Track Troubles

Hurricane Irma remains an extremely powerful and dangerous category 5 hurricane, after passing over St. Martin this morning.

Source: NOAA/NWS/National Hurricane Center

Here's a shot as the system passed over Barbuda overnight.

Source: NOAA/NWS/National Hurricane Center

Wind observations from Barbuda show the remarkable increase in wind speed with the approach of the eye, reaching a maximum sustained velocity of nearly 120 mph and a peak gust of 155 mph before the sensor gave out.

Source: MesoWest

These are simply incredible numbers, especially that the winds at the time were out of the north and the site is on the south side of Barbuda.

From now through Saturday, the center of Irma is expected to track just to the north or along Puerto Rico, the Dominican Republic, Haiti, and eastern Cuba.

Source: NOAA/NWS/National Hurricane Center

Forecasts for Florida and the southeast US are remarkably tricky and depend strongly on when Irma takes the anticipated northward shift in track.  To highlight the abrupt nature of the anticipated track shift, I've put together a loop of the GFS forecast below (based on lower resolution grids).  Note the very steady WNW progression of Irma until it approaches the Florida Peninsula, when it decides to alter course and move northward.

The loop above is just one model solution.  Below shows the tracks produced by the GEFS ensemble, which fan out from the eastern Gulf of Mexico to tracks that don't even reach the US mainland.

Source: Tropical Tidbits

Forecasters will have these and additional tracks from the ECMWF and Hurricane models to ponder.  Today's forecasts are especially critical given the long time scales needed for hurricane preparation and evacuation from the Keys and South Florida. Keep in mind that we are still talking about a 4-5 day forecast from now until Irma is flirting with Florida.  The issues at play at these lead times are well summarized by the 5 AM AST forecast discussion from the National Hurricane Center.

Source: Source: NOAA/NWS/National Hurricane Center

The bottom line is that there is a wide range of possible tracks, and as a result, details of the timing and magnitude of Irma's impacts on Florida and other southeast US states remain uncertain.