30 September 2022

Ian's third and final landfall in South Carolina

Fifteen days after leaving the African coast, Ian's last few hours are here.  It became a tropical depression on the 23rd, made landfall in western Cuba as a Category 3 hurricane on the 27th, then in central Florida as a Category 4 on the 28th, and now in South Carolina as a Category 1 on the 30th.

Although Ian is on the cusp of becoming an extratropical cyclone, it still poses the same threat (remember Sandy in 2012?).  It's a Category 1 hurricane with 85 mph peak sustained winds, and made landfall between Charleston and Myrtle Beach on Friday afternoon at about 2pm local time.  Ian will dissipate over the Carolinas and Virginia in the next day or so, and after dropping a few inches of rain over those areas, that will be the end of it.

Storm surge was and is the primary threat today, and some areas have definitely experienced severe coastal flooding today.

There is another wave of interest just moving off the African coast today.  Like Ian, it's coming off at a very low latitude, but unlike Ian, it's likely to turn to the northwest within a week.  After that, there's some divergence in the model guidance so it's just something we'll need to keep an eye on now and then -- it's very far from any land.  If it becomes a tropical storm, the next name is Julia.

September was extremely active... of the nine named storms so far this season, six of them formed in September.  In terms of ACE, September accounts for 94% of the total at this point, two-thirds of the way through the season.  And compared to the average over the past fifty years, 2022 is now at 97% of the average value for the date.

As of Friday afternoon, these next two images show the history of NHC forecasts for Ian: track on top then intensity below.  The observed track and intensity is the thick black line, and each six-hourly forecast is shown by a colored line.

As it relates to the Florida landfall, the "cone of uncertainty" always contained the eventual landfall point... every advisory for all five days from Ian's formation on the 23rd to its landfall on the 28th.  The cone is designed to show where the center of the storm should track, with 2/3 likelihood.  Having that long to prepare for what was forecast to be a major hurricane landfall is very good, but it doesn't stop the damage from happening, unfortunately.  All people can do is get out of its way.

29 September 2022

Back over water, Hurricane Ian is poised to make yet another landfall

After making landfall as an upper-end Category 4 hurricane on Wednesday afternoon, Ian took its time traversing the Florida peninsula.  It briefly weakened to a tropical storm, but the center of now Hurricane Ian re-emerged over the Atlantic Ocean midday Thursday.  It's interacting with a mid-latitude trough that is stretching its cloud shield out to England.  No, seriously... England!

This 3-day radar animation is quite amazing in what it covers in the lifecycle of a tropical cyclone.  You can find this and others at http://bmcnoldy.rsmas.miami.edu/tropics/radar/

Although Ian is back over water, it's in a very different environment than it was before reaching Florida.  It's now in high vertical wind shear and is well on its way to becoming an extratropical cyclone.  But before it does so, it regained hurricane status today before making landfall in South Carolina midday Friday.

Regardless of the exact intensity, the outcome will be the same.  It will create a fairly high storm surge of 4-7 feet in the central part of the state, as well as 6-10 inches of rain.  This won't be nearly as severe of a landfall as the one in Cuba or Florida, but it is still extremely dangerous and life-threatening.  Seven feet of ocean coming at you with angry waves on top is very serious.

The current suite of Hurricane Threat & Impacts is shown here, and the "cone of uncertainty" is overlaid for reference.  Keep in mind that the cone is ONLY designed to show you where the center of the storm might track (with 2/3 probability).  Impacts can and always do extend far beyond the cone.

Now that' we're headed for a bit of reprieve in activity, here's an update on where the season stands in terms of Accumulated Cyclone Energy.  The current total is about 96% of average for this date if we use the past fifty years as the baseline.  The very quiet first half of the season was met with a very active September (the average ACE  September is 50 and we're at 74).

28 September 2022

Ian makes landfall as upper-end Category 4 hurricane in Florida

Unfortunately, the expectations of rapid intensification in the eastern Gulf of Mexico were met and even exceeded.  Ian left the northern coast of Cuba as a low-end Category 3 hurricane and hit the west-central Florida peninsula as an upper-end Category 4 hurricane, just 7 mph shy of Category 5 status.  The landfall point is where the center of the eye crosses the coastline, and that was right by Boca Grande, which is about 25 miles north of Fort Myers and 40 miles south of Sarasota.

Keep in mind that a post-season reanalysis is always performed and intensities assigned operationally can be adjusted up or down as necessary.  It's possible that Ian was a Category 5 hurricane, it just takes more scrutiny of observations and hindsight than real-time work allows.

For those not familiar with the layout and city names in the area, this map provides a reference, with the approximate landfall point marked by a red dot and the eyewall by a red circle.  Areas just south of the landfall point such as Cape Coral, Fort Myers Beach,  and Fort Myers experienced the southern eyewall, the full power of the hurricane with onshore winds... maximum wind and storm surge.

Breaking down some numbers, here is an abridged timeline of peak sustained winds (times are EDT, intensities are mph):
Sun 11pm - 65 mph tropical storm
Mon 5am - 75 mph Category 1 hurricane
Mon 5pm - 100 mph Category 2 hurricane
Tues 5am - 125 mph Category 3 hurricane, landfall in Cuba
Tues 11am - 115 mph Category 3 hurricane, exiting Cuba
Wed 5am - 140 mph Category 4 hurricane
Wed 9am - 155 mph Category 4 hurricane
Wed 3pm - 150 mph Category 4 hurricane, landfall in Florida

The hurricane went through an eyewall replacement cycle on Tuesday evening into Wednesday morning... this is a typical process that intense hurricanes go through.  The big picture is that the storm's eyewall contracts, dissipates, and gets replaced by a larger eyewall.  Hurricanes tend to weaken slightly during this transition, but once it's complete, the overall wind field expands and the storm is primed to re-intensify.  That's exactly what Ian did, and it did so just hours before making landfall.  In this 36-hour animation from the Key West radar, you see Ian's eye pass over western Cuba, then the eyewall falls apart and a new larger one replaces it.

It's hard to say now what the aftermath will look like near the landfall point, but it's impossible for it to not be catastrophic.  The last storm surge forecast made before landfall included 12-18 feet in the Charlotte Harbor area, then decreasing away from there, but still extremely high.  Wind gusts are estimated to be around 190 mph in the eyewall.

The rainfall forecast is also extreme in central Florida, and high totals extend up into the eastern Carolinas over the next few days as Ian makes its way northeast.  It will travel slowly across the Florida peninsula, passing near Orlando and Jacksonville along the way, then re-emerge back over the ocean briefly on Thursday night to make another landfall (MUCH weaker) in Georgia or South Carolina on Friday evening.

Looking back, the track forecasts from the National Hurricane Center were remarkably consistent; the eventual landfall point in Florida was in the "cone of uncertainty" for Ian's entire life, going back to when it formed last Friday.  Just looking at the past three days, this graphic shows every cone overlaid on each other, with the most recent (Wednesday morning) in orange.  Keep in mind that the cone is designed to show where the center of the storm might track, with 2/3 probability, and does not tell you where impacts will be experienced.  [see "Cone of Uncertainty Update & Refresher"]

Elsewhere across the basin, Tropical Depression 11 formed today in the central Atlantic, but will be very short-lived and I won't go into more detail on it unless it ends up becoming a named storm.  If it does, the next name is Julia.

27 September 2022

Major Hurricane Ian crosses Cuba and enters Gulf of Mexico

As expected, Ian rapidly intensified and became the season's second major hurricane on Tuesday morning.  (A "major hurricane" is simply defined to be a Category 3+ hurricane on the Saffir-Simpson Scale).  It crossed the western tip of Cuba and the eye is now back over water.  It is forecast to make landfall in the Tampa area as a Category 3-4 hurricane on Wednesday night.

Zooming in on the eye, it's amazing to watch it quickly clear out after leaving Cuba -- Ian wasted no time re-intensifying and it's undoubtedly well on its way to becoming a Category 4 hurricane.

Ian has been in continuous radar coverage since Sunday morning, and you can find the archived and current radar loops at http://bmcnoldy.rsmas.miami.edu/tropics/radar/.  This view shown below is a mosaic of many radars to create a regional-scale image.

It has now been 12 days since Ian left the African coast as an easterly wave, and 4 days since it became a tropical cyclone.  Now the final days are here, and they are extremely impactful.  Tropical storm, hurricane, storm surge, flood, and tornado watches and warnings plaster nearly all of Florida and even into Georgia and South Carolina.

The Tuesday afternoon suite of Hurricane Threats & Impacts (HTI) graphics are shown here.  These break the hurricane down into its four hazards (wind, surge, rain, and tornado) and provide relative threat levels from each hazard.  As you can see, the entire peninsula will experience impacts from Hurricane Ian, but the worst is focused on the central part of the west coast.  If you are anywhere that's covered by a threat in red or purple, be prepared for some serious and even life-threatening impacts from the corresponding hazard.

As far as winds go, tropical storm conditions will gradually work their way northward along the peninsula, beginning with Key West this afternoon, and wrapping up around Jacksonville on Thursday morning.  Although not shown here, the hurricane's large wind field will amplify coastal flooding issues on the east and west coasts... water levels were already running high because of the new moon and time of year.  The storm surge near landfall is quite different; that is far more dire and life-threatening than elevated tides elsewhere in the state.

Between the landfall in Cuba and then in Florida, there's little doubt that the name Ian will be retired after only its second use (it replaced Igor in 2016).  This would make it the 13th "I" name to be retired since tropical cyclones were given names in the Atlantic, by far more than any other letter.  To make the "Curse of the I" more complete, it's also in September and it's also likely going to peak at Category 4 intensity -- all three of these traits reinforce the existing leaders of retired names.

26 September 2022

Hurricane Ian heading for Cuba and Florida

Since my last post on Friday, Fiona made landfall in eastern Nova Scotia as an extratropical cyclone of Category 2 hurricane intensity, Tropical Storm Gaston dissipated west of the Azores, Tropical Depression 10 became Tropical Storm Hermine northeast of Cabo Verde and is already gone, and Tropical Depression 9 became Tropical Storm Ian on Friday night then Hurricane Ian on Monday morning.  This update will focus solely on Hurricane Ian.

As of Monday morning, Ian is centered just 80 miles west of the Cayman Islands and 250 miles southeast of western of Cuba.  There is strong agreement among the model guidance that Ian will quickly reach major hurricane status (the second of the season) perhaps tonight or Tuesday morning as it nears western Cuba.  That brief interaction, though extremely high-impact for Cuba, should not disrupt the hurricane too much, so additional strengthening is likely once it's in the eastern Gulf of Mexico by midday Tuesday.

The biggest concern for both Cuba and the west coast of Florida is storm surge.  Cuba could be looking 9-14 feet of storm surge east of where the eye crosses the coast, and although preliminary, the 2-3-day storm surge outlook for the southwestern Florida peninsula is shown below.  As the storm gets closer, the storm surge guidance will become more accurate and include areas farther north into the Big Bend area.  Because of its shape, Tampa Bay is very surge-prone, so the storm's size, intensity, heading, and distance from land will determine if this is a very bad or a catastrophic event there.

The intensity forecast from NHC this morning explicitly includes rapid intensification, a very rare amount of confidence.  By design, "rapid intensification" (RI), is the top 5% of intensification rates, and objectively, the common definition is an increase of 35 mph or more in a 24-hour period.  Here's the forecast from 5am today:
INIT  26/0900Z 18.2N  82.0W   65 KT  75 MPH
 12H  26/1800Z 19.7N  83.0W   90 KT 105 MPH
 24H  27/0600Z 21.7N  83.9W  105 KT 120 MPH (+45mph in 24hr)
 36H  27/1800Z 23.6N  84.1W  115 KT 130 MPH
 48H  28/0600Z 25.3N  84.1W  120 KT 140 MPH
You may recall that the same degree of confidence was shown in the initial forecast for Hurricane Ida last year.  Such confidence in an outlier event is a success story of hurricane modeling in the past decade or so.

In the Florida peninsula, tropical storm force winds could reach south Florida Tuesday night into Wednesday morning, central Florida Wednesday morning to Wednesday afternoon, and northern Florida Thursday morning.  The western part of the peninsula is more likely to encounter those winds and is on the earlier end of the ranges I mentioned.

In addition to the winds and storm surge associated with a strong hurricane, rainfall is always a significant threat with any tropical cyclone.  The map below is the five-day rainfall forecast and there are significant amounts expected in the entire Florida peninsula, then up into eastern Georgia and South Carolina later in the period.

Elsewhere, there is another wave behind Ian, about 1600 miles east of the Lesser Antilles.  This is tagged as Invest 99L, and although favored to develop soon, it's forecast to move north and dissipate over the central Atlantic.  The next name on the list is Julia.

With all of the named storms scattered across the basin, the season's total Accumulated Cyclone Energy has gotten a big boost and is now at 84% of the average value for this date.  Hurricane Ian will add to the tally quite a bit in the coming 3-4 days.

23 September 2022

A major hurricane, tropical storm, and two tropical depressions scattered across the Atlantic

Fiona is still a Category 4 hurricane... it passed west of Bermuda and is now headed for Nova Scotia.  Gaston is still a tropical storm, drifting around the Azores, Invest 98L was upgraded to Tropical Depression 9 on Friday morning, and Invest 90L was upgraded to Tropical Depression 10 on Friday morning.

Overview of Atlantic tropical cyclones and Invests, courtesy of Tomer Burg.

Unfortunately for eastern Canada, Fiona has not unexpectedly weakened or deviated from the forecast track.  It is set to make a historic landfall early Saturday morning... perhaps as the strongest storm the area has ever experienced.  Although the storm will transition to an extratropical cyclone before reaching Canada, the impacts will remain the same; it will be an extratropical cyclone with sustained winds of 100 mph or so. The storm surge and resulting coastal flooding will be significant in coastal areas east of the center.

Not only it is a Category 4 hurricane now, it will gain energy from interaction with a trough, a process known as "baroclinic enhancement".  This process is fairly typical for high-latitude storms, but this is going to be an exceptional example.  You can find a radar loop of Fiona's encounter with Nova Scotia and Newfoundland at http://bmcnoldy.rsmas.miami.edu/tropics/radar/

Similar to yesterday, Gaston is a mid-rage tropical storm, now in the midst of the Azores and expected to stall for the next 2-3 days, then draft was toward the west as it weakens and loses its tropical characteristics.

Invest 90L, the one that was on the coast of Africa yesterday, was upgraded to TD10 today, based on rare but valuable aircraft reconnaissance by the NASA DC-8 aircraft based in Cabo Verde for a field program.  Although this could become a tropical storm very soon, its future is limited and is expected to dissipate by the end of the weekend.

As I wrote yesterday, I found just three other examples of this happening (a wave coming off of Africa, developing, and turning north, all before reaching Cabo Verde): Tropical Storm Becky in 1962, Tropical Storm Ginger in 1967, and an unnamed tropical storm in 1988.

Finally, Invest 98L, the wave that left the African coast back on September 15, was upgraded to Tropical Depression 9 early Friday morning and is now centered about halfway between Venezuela and Hispaniola.  It's still experiencing hefty vertical wind shear -- in this satellite animation, you see all of the thunderstorm activity getting pushed to the southwest, leaving the low-level center completely exposed.

The bad news is that the wind shear is forecast to become quite low starting on Saturday and lasting through Tuesday.  At the same time, it will be passing over incredibly favorable ocean conditions in the western Caribbean.  There is the potential for some very rapid intensification over the weekend as it passes near Jamaica on Sunday morning then into western Cuba midday Monday.

The NHC forecast as of 11am EDT Friday brings it to Category 2 intensity when it's near Cuba, then Category 3 intensity when it's near south and central Florida on Tuesday night into Wednesday morning.  But that all assumes it won't rapidly intensify over the western Caribbean this weekend.  For anyone in western Cuba and south/central Florida, I'd take this threat very seriously.

Tropical storm force winds could arrive in Cuba midday Monday, Tuesday morning in south Florida, and Tuesday afternoon in central Florida.  You want to have all outdoor preparations complete by then.

The next two names on the list are Hermine and Ian, and it will be a race between TD9 and TD10 for which name goes to which storm.

Thanks to Fiona, the season's total ACE (Accumulated Cyclone Energy) got a huge push, bringing it up to about 82% of average for the date.  So far, that single storm has contributed 43% of the total, and it's still going.

22 September 2022

Little change in overall activity since Wednesday

I will keep today's update relatively brief... although there is a lot of activity across the basin, none of it has evolved much since yesterday's post.  Fiona is still a Category 4 hurricane about to pass close to Bermuda, Gaston is still a meandering tropical storm near the Azores, and none of the three areas of interest in the deep tropics have become tropical cyclones yet.

Large-scale satellite image of the Atlantic basin. Hurricane Fiona and Tropical Storm Gaston are the top, while Invest 98L, 99L, and 90L are circled along the bottom.

Fiona continues to be a very powerful hurricane... it's now been a major hurricane for 2.5 days and it has more to go.  It will pass just west of Bermuda tonight, close enough to produce destructive winds and storm surge.  Peak sustained winds are still at 130 mph and tropical storm force winds extend an average of 175 miles from the center.  In the loop below, Bermuda is the white speck northeast of Fiona's center.

The upcoming landfall in eastern Nova Scotia on Saturday morning is still expected to be historic.  As I mentioned yesterday, the storm could break all-time record-low surface pressure values there, and with forecast sustained winds of 90 mph, it will also be one of the most intense storms that area has ever seen... comparable to Juan in 2003 which made landfall on the western end of Nova Scotia.

This most recent run of the HWRF model brings it to landfall with a central pressure of 914 mb, which is just unthinkable.  For perspective, at lower latitudes that would be a Category 5 hurricane.  This will be a storm for the Canadian history books.

I'm going to skip over Gaston and Invest 99L today and move on to Invest 90L next, which is the disturbance right on the coast of Africa.  NHC is giving that a 60% probability of becoming a tropical cyclone within the next couple of days, but not only is it REALLY far east, the forecast is for it to move north!  

I found just three other examples of this happening (a wave coming off of Africa, developing, and turning north, all before reaching Cabo Verde): Tropical Storm Becky in 1962, Tropical Storm Ginger in 1967, and an unnamed tropical storm in 1988.

In the satellite loop below, you can see that it has a very limited future -- it's ingesting huge amounts of dry, dusty Saharan air.

Finally, Invest 98L continues to hug the coast of Venezuela and is about to pass just north of Bonaire, Curacao, and Aruba.  All of the model guidance indicates that it will begin to drift north away from land, gradually escape the strong wind shear, and likely become a named storm by Sunday when it's south of Jamaica.  As hostile as the environment is now, that is likely to change real fast this weekend.

The magnitude of the vertical wind shear is expected to be half of what it is now by Sunday, and half of that again by Wednesday. The images below show the sea surface temperature and the ocean heat content as alternating frames to illustrate where the water is warmest AND where that warm water extends the deepest (ocean heat content values are missing where the water is too shallow).  The western Caribbean is primed for whatever comes its way. 

I'll use the same format of track forecasts as before to make comparisons easier.  The European model's ensemble is on the left and the American model's ensemble is on the right.  I'll point out that the European ensemble has not moved much, while the American ensemble has drifted westward over the past few cycles.  Although not shown, the deterministic runs from the global models are not shy about creating a powerful hurricane by Monday.  Most favor tracks toward Cuba and then Florida, while the American model tracks the storm into the central Gulf and north from there.

As before, anyone in the Yucatan, Jamaica, Cuba, Florida, and the northern US Gulf coast should be paying close attention and be prepared to begin preparations as the track forecasts narrow.  This could be the type of storm that takes a long time to finally form but when it does, there's a short fuse until it makes landfall somewhere as a hurricane.