29 September 2015

Joaquin forms near Bahamas, could threaten northeast U.S.

On Sunday night, Tropical Depression 11 formed north of the Bahamas, and on Monday night it was upgraded to Tropical Storm Joaquin, the tenth named storm of the season.  It is currently centered about 400 miles north of the eastern Bahamas and is drifting west.

Joaquin actually was born of an upper-level low that sat nearly stationary for over a week and gradually built down to the surface and acquired tropical characteristics.  Evidence of the upper-level low extends back to beyond September 20!  In this figure, there are slices of infrared satellite images shown every 12 hours for a week, and you can spot the same feature at nearly the same location east of the Bahamas the entire time.

It is in an area with minimal steering flow, so it is not forecast to move much in the next couple of days.  By Thursday, it should begin to feel a trough approaching the area and start to turn to the north.  However, there is tremendous spread among the reliable models even in the near future (1-3 days), so the timing is quite uncertain.  But, aside from the timing, there is decent agreement a general track to the north and then toward the northeast U.S. coast.

Track forecasts from a variety of global and regional dynamical models and consensus from the 06Z guidance. (UWM)
The intensity forecasts, for the most part, indicate that Joaquin will become a Category 1-2 hurricane around Friday.  Some models are significantly stronger, and few are weaker (AVNI and NVGI are global models, and have a harder time with intensity because of their coarser resolution).

Intensity forecasts from a variety of global and regional dynamical models, statistical-dynamical models, and consensus from the 06Z guidance. (UWM)
The official forecast from the National Hurricane Center is shown here, which generally agrees with the model consensus for track, but is a bit lower than the model consensus for intensity.

Vertical wind shear will be fairly strong over Joaquin until Thursday or so, which will be a key day to see if it intensifies quickly or not... because once it starts interacting with the trough that is expected to come off the east coast, the shear will increase again. 

However, and this is really important, if it begins to lose tropical characteristics as it heads north, that does not make it less dangerous should it make landfall.  A Sandy-like scenario is not something I'd predict this far out, but it's also not completely impossible and is something to be aware of.  There are a lot of unknowns to be resolved before being too concerned about that possibility.

23 September 2015

Okay, so I'm a geek.

This is an atypical and hopefully entertaining post... after being asked by several people about a particular "honor" bestowed upon me recently, I figured I might as well share.
The Weather Channel has a television program (it airs Sundays at noon eastern) called Wx Geeks.  For each episode, they select a "Geek of the Week", which is just a fun thing they do.  Well, lo and behold, I was that person this week.

The blurb that was on tv is available at https://www.youtube.com/watch?v=s_a49kYeAZY

You can also view the whole interview with photos on Facebook at https://www.facebook.com/WXGeeksTWC/posts/814677201979434

So there you have it!

21 September 2015

Ida strengthens in central Atlantic

Since my last update on Wednesday the 16th, Tropical Depression 9 dissipated on Saturday.  The wave behind it was upgraded to Tropical Depression 10 on Friday morning, and later upgraded to Tropical Storm Ida on Friday night.  Ida is the season's ninth named storm.  Using 1981-2010 as the climatology, the ninth named storm forms on September 29 during an average season.

Ida has not done much though, as it turned to the northwest and encountered strong vertical shear. However, environmental conditions have been improving and Ida has strengthened as a result.  As of Monday morning, peak winds are estimated at 50mph.  It is forecast to remain nearly stationary but also to gradually intensify over the next five days. While it does stand a chance of becoming the season's third hurricane, it is not a threat to land.

Elsewhere, no new formation is expected this week.  But global models are in agreement on something brewing in the southern Gulf of Mexico this weekend, and generally tracking it northward.  This is absolutely not a cause for concern, it is just something to monitor in the models for now... the disturbance doesn't even exist yet.  Below is output from three global models (ECMWF, GFS, and CMC), all valid on Sunday evening.  The colored field is the 850mb vorticity, which is a measure of the curvature of the low-level wind.

850mb vorticity from the 00Z runs today, valid in seven days.  ECMWF is on the left, GFS is in the middle, and CMC is on the right. (tropicaltidbits.com)

16 September 2015

Tropical Depression 9 forms in central Atlantic

As I described in Monday's update, the easterly wave that was near 38°W was just upgraded to Tropical Depression 9.  It was a bit slow to get organized, but it did track northwest as expected.  It's currently centered about 1200 miles east of the Lesser Antilles and moving north-northwest at 8 mph.

It is entering a more hostile environment, so it may not be around long, and it won't get near any land or islands. If it should manage to sneak up to tropical storm intensity, the next name is Ida.

And, same as on Monday, there is a potent easterly wave right behind it which could become TD10 (or the next name after Ida is Joaquin) this week too.

This disturbance is also forecast to recurve by 45°W, and perhaps strengthen slightly in the coming days.

14 September 2015

Disturbance in central Atlantic expected to become TS Ida

An easterly wave that exited the African coast last Thursday has gotten slightly better organized and could become Tropical Depression 9 later today or tomorrow.  It is currently centered about 1400 miles east of the Windward Islands and is moving toward the northwest.  If it eventually becomes a tropical storm, the next name on the list is Ida.  However, as of Monday morning, it is decidedly not an impressive feature on satellite images... it's a tiny swirl with minimal thunderstorm activity.  In fact, it's hard to find unless you know where to look!  In the satellite image below, I drew an arrow pointing down to the feature of interest.

Model guidance predicts that this disturbance will become a tropical storm within the next 1-2 days, and turn to the north by the time it reaches around 45°W, keeping it far away from any land.

Further east, another easterly wave has just exited the African coast and models strongly favor its development as well.  Like the one to its west, this would also very likely recurve to the north long before reaching any land areas.  But, if it also develops into a tropical storm, the name after Ida is Joaquin.

10 September 2015

After Further Review: Tropical Storm Erika

A second post today, but this one is actually a look back at Erika.  Erika presented the media and forecasters with challenges, but none that were unexpected.  If you live in Florida, or any hurricane-prone coastal area for that matter, this National Hurricane Center blog post is a must-read.  Understanding forecast uncertainty is critical, and unfortunately, you won't typically hear about it on the news.

After Further Review: Tropical Storm Erika

Tropical Storm Henri forms near Bermuda at typical peak of Atlantic hurricane season

Today's update is available on the Washington Post's Capital Weather Gang blog:

Tropical Storm Henri forms near Bermuda at typical peak of Atlantic hurricane season

06 September 2015

Fred and Grace spinning in far eastern Atlantic

On Saturday afternoon, Fred was downgraded to a Depression, again.  As of Sunday morning, it remains a Depression, but is forecast to regain tropical storm status by Tuesday as it moves toward a more favorable environment.

It has been a tropical cyclone for almost 8 days, and apparently, the normal environmental thresholds for TC maintenance don't apply to Fred, so it could be around for quite a while longer!  It has begun recurving to the north, and is forecast to head toward the northeast over the next 5 days.

As I hinted at in Friday's update, Grace is indeed now an active storm.  An easterly wave that left the African coast on Thursday became Tropical Depression 7 on Saturday morning, and then was quickly upgraded to Tropical Storm Grace on Saturday afternoon.  Grace is the 7th named storm of the 2015 season, and climatologically, the 7th named storm forms on September 12.  However, in terms of ACE (Accumulated Cyclone Energy), the season is still only at about 55% of average for this date.

Large-scale visible satellite image of Grace from 9:15am EDT today.  The Cape Verde islands are to its northeast. The milky color to the west and north of the storm is indicative of dusty, dry, stable air from the Sahara. (NRLMRY)
Grace is on a strengthening trend, and is tracking west at 13 mph.  For reference, it is located about 1200 miles southeast of Fred.  Models generally agree that it will reach the Leeward Islands region in about 6 days (Saturday-ish).  Here I show a selection of global and regional dynamical model 5-day forecast tracks, as well as the NHC forecast (OFCI).

However, it will be slamming into a wall of strong vertical wind shear on Wednesday, which should quickly put an end to any intensification that may occur in the meantime.  Models are currently in unanimous agreement on this.  The map below shows the forecast wind shear valid late Wednesday night.... Grace is the 1008mb Low that you see just east of the Lesser Antilles, nestled right up into the subtropical jet.  Typically, wind shear over 20kts is detrimental to tropical cyclones, so the 40kt+ swath cutting through the tropics would certainly have an impact on it.

04 September 2015

Fred STILL not dead, and future Grace brewing in eastern Atlantic?

Much to the surprise of forecasters, Fred remains a minimal tropical storm on Friday morning, being sustained by intermittent bursts of strong thunderstorms near the center.  It's barely clinging to tropical cyclone status amidst very strong wind shear, dry air, and marginal ocean temperatures. The forecast continues to indicate Fred dissipating to a remnant low, but we shall see.  Several models actually indicate that it could re-strengthen in about 4-5 days as it turns toward the Azores, so we could still be talking about Fred at this time next week!

Visible satellite view of Tropical Storm Fred from 7:45am EDT today.
5-day forecast track of Fred, or whatever is left of it, from the 5am EDT advisory. (NOAA)

Elsewhere, an easterly wave that exited the African coast yesterday is showing signs of development.  It is currently centered about 350 miles southeast of the Cape Verde Islands, and about 2800 miles east of the Windward Islands.

It is likely going to track toward the west-northwest over the next 5 days as it gradually organizes.  It could become Tropical Depression 7, and then the next name on the list is Grace.  Just for reference (this isn't a forecast), the average easterly wave travel time from this location to the Lesser Antilles is roughly seven days.

02 September 2015

Fred weakening, and 80th anniversary of Labor Day Hurricane

Since my last update on Monday morning, Fred has weakened to a 45mph tropical storm and is quickly on the way to becoming a remnant low.  The Big 3 environmental factors for tropical cyclone intensity (sea surface temperature, wind shear, and low-level humidity) are all plunging into ranges that have caused Fred to quickly dissipate.  All that remains is a low-level swirl northwest of the Cape Verde Islands.  Although it was a short lifetime, it was the easternmost Cape Verde hurricane on record, which is certainly noteworthy.

Elsewhere across the Atlantic, there is nothing brewing in the foreseeable future.  This is a bit unusual as we ramp up to the climatological peak of the season!

Daily climatology of Accumulated Cyclone Energy (ACE).
Tonight is a very special anniversary... 80 years ago on the night of September 2, the most intense Atlantic landfalling hurricane on record hit the upper Florida Keys (Long Key): the infamous 1935 Labor Day Hurricane.  It made landfall with sustained winds of 185 mph and produced an 18-foot storm surge in the upper Keys.  It's worth pointing out that it was a tropical storm just 44 hours prior, so yes, tropical cyclones are capable of incredible intensification rates when conditions are ideal.  Even in 2015, I can say with confidence that we could not predict this super-rapid intensification.

Track of the 1935 "Labor Day" hurricane, which remains the most intense landfalling hurricane anywhere in the Atlantic.
If you use Facebook, my friend and hurricane historian Michael Laca has an excellent collection of photos and information from the storm: https://www.facebook.com/media/set/?set=a.220683491357229.52229.218869288205316&type=3&pnref=story

There's a beautiful memorial in Islamorada (which was completely obliterated that night) to commemorate the approximately 400 people who died in the storm... here is a photo taken by Michael.  The plaque at the base of the monument reads: "Dedicated to the memory of the civilians and war veterans whose lives were lost in the hurricane of September Second, 1935."

The 1935 hurricane memorial in Islamorada, FL.  Photo by Michael Laca.