30 September 2016

Matthew explodes into major hurricane

Hurricane Matthew has rapidly intensified, and is now a Category 3 storm packing 115 mph winds.  You can read my full update on the Capital Weather Gang blog:

Matthew explodes into major hurricane

29 September 2016

Matthew strengthens to a hurricane as it traverses the Caribbean

Matthew now has peak winds of 75 mph, making it the fifth hurricane of the season.  It is centered about 300 miles south of San Juan, and tracking west at 15 mph.

The storm has encountered unexpectedly high wind shear, which has slowed down its intensification rate, but it is still managed to achieve hurricane intensity.  It is the season's fifth hurricane, and only the fifth hurricane to form in the Caribbean in the past five years (the others were Rina '11, Ernesto '12, Sandy '12, and Gonzalo '14).

A band of strong wind shear lies ahead of it now, which is actually not uncommon in the central Caribbean... but it should pass through it by Saturday.

As mentioned yesterday, the long-range forecast track is rather similar to Hazel (1954), but if we start the comparison from the point where Matthew should turn northward, the forecast track out to 5-7 days also resembles Sandy (2012).

Matthew is still expected to continue its westward track through the Caribbean for another 2-3 days, then the model guidance starts to diverge.  Some models immediately commence with a northward turn, while others leave it lingering in the Caribbean for at least another day or two, delaying the turn and reducing the predictability.

In this plot of model runs from late last night, the tracks appear to be somewhat clustered, but the timing is quite different.  I used this map rather than the most recent because it includes a leading global model, labeled ECMF on here (dark red line).  Notice that both the ECMF and UKM lines show a track that is further south and much slower than the others.  Any time a tropical cyclone is moving very slowly, it is a sign of weak steering currents and relatively low predictability.

In terms of intensity, nearly all models agree that it will maintain hurricane intensity through the weekend, and then strengthen some more as it heads for Haiti/Jamaica/Cuba.  The official NHC 5-day forecast is shown here:

Some key "cone of uncertainty" refreshers:

1) The cone does not indicate the actual level of confidence or predictability.  The cone is a fixed size all season long, for all storms and all forecasts.  In some situations, the realistic uncertainty in the track forecast is greater than what the cone portrays, and sometimes it's less.

2) The cone is only designed to enclose the storm's position with 2/3 probability... there is historically a 1/3 chance the center will track outside of the cone.

3) The cone does not indicate where the impacts will be experienced.  Impacts from a hurricane will extend beyond the cone, even for a perfect forecast.

For now, any U.S. impacts are too uncertain to worry about, and would be at least 5-6 days away at the earliest (south Florida would be the closest).  But in the shorter term, Jamaica, Haiti, and Cuba are in Matthew's sights early-mid next week, and heavy rain is a risk even far from where the center tracks.

28 September 2016

Tropical Storm Matthew forecasts are eerily similar to Hurricane Hazel in 1954

As promised, the second post today revisits the 1954 hurricane season, one that changed how the United States views the threat of hurricanes and funds the science to better predict them.  One storm from that infamous season was Hazel, which took a track that closely resembles the long-range model guidance for recently-formed Matthew.  The post is available on the Capital Weather Gang blog:

Tropical Storm Matthew forecasts are eerily similar to Hurricane Hazel in 1954

Tropical Storm Matthew forms and enters Caribbean

The disturbance we've been tracking since Friday was upgraded to Tropical Storm Matthew today, just as it crossed the Windward Islands and entered the eastern Caribbean Sea.  There will be two posts on it today, the first covers the storm and forecasts, while the second one will explore a haunting similarity that Matthew's forecast track has with an infamous storm from 1954: Hurricane Hazel.  Thanks for reading and sharing!

Tropical Storm Matthew may pose a threat to the U.S. coast next week

23 September 2016

Karl strengthens, hurricane watch issued for Bermuda

Both Karl and Lisa are still active, but Karl is taking the spotlight as it approaches Bermuda.  It is also on an intensification trend, and could become the season's fifth hurricane later today or tomorrow.

Satellite image of Tropical Storm Karl.  Bermuda is the magenta speck just north of the center of the image.
As of 11am EDT, Karl's maximum sustained winds were 60mph, and it had begun the turn to the north... moving north at 12 mph.  It will make its closest approach to Bermuda tonight, and Bermuda is under a tropical storm warning and a hurricane watch. I have long, updating radar loops available at http://andrew.rsmas.miami.edu/bmcnoldy/tropics/radar/

There are four aircraft monitoring this storm through the day and night: the NOAA P-3 and AF C-130 (they fly right into it to gather key data about the vortex), and the NOAA G-IV and NASA's unmanned GlobalHawk (they fly over and around it to gather environmental data).

Further east, Lisa is barely clinging to tropical storm status as it faces strong wind shear.  The satellite appearance tells the story: the low-level circulation is completely exposed, and the little thunderstorm activity that is still occurring is displaced far to the northeast. It is forecast to weaken to a tropical depression later today, and then dissipate completely sometime tomorrow.

Finally, another easterly wave just exited the African coast on the 22nd.  It doesn't look like much now, but global models have been bullish on developing this one in the deep tropics in 5-7 days and tracking it through the Caribbean.  More on this next week... the next name on the list is Matthew.

20 September 2016

Lisa forms in eastern Atlantic, Karl may threaten Bermuda

Although very little has changed with Tropical Storm Karl, the disturbance I've been mentioning since last Friday was upgraded to Tropical Depression 13 on Monday afternoon, and then again to Tropical Storm Lisa on Tuesday morning.  Lisa is the season's 12th named storm, while in an average season, only 12 named storms form through the end of November!

Tropical Storm Lisa on Tuesday morning.
Lisa is centered just west of the Cabo Verde Islands, and is forecast to turn toward the northwest and head into a more hostile environment.  It may have the next few days to exist as a tropical storm, but model guidance and the NHC forecast indicate that it will weaken this weekend.  It is no threat to land.

About 1500 miles to the west, Tropical Storm Karl remains somewhat disorganized and sheared, but is expected to strengthen in a couple days as it recurves toward Bermuda.

Tropical Storm Karl... the yellow shading highlights low-level clouds and the white indicates higher clouds associated with thunderstorms.
The map below shows track forecasts from a variety of regional and global dynamical models, and while the recurvature scenario is extremely likely, the exact timing will determine how close the storm gets to Bermuda.  As I mentioned yesterday, Bermuda has had three hurricanes pass very close in the past couple of years: Joaquin '15, Gonzalo '14, and Fay '14.

As it looks now, Bermuda has a very high chance of experiencing at least tropical storm force winds.  NHC forecasts Karl to reach hurricane intensity by Friday, and perhaps reach Category 2 status by Saturday as it passes by Bermuda.

19 September 2016

Karl still a tropical storm, and Lisa could form later today

Since my last update on Friday morning, the only remaining features of interest are Tropical Storm Karl and Invest 96L.  Both are located in the central and eastern Atlantic and do not pose a threat to land in the near future.

Tropical Storm Karl is centered about 900 miles east of the Leeward Islands and moving toward the west at 15 mph.  Environmental conditions are expected to gradually become more favorable for some strengthening this week, and the National Hurricane Center forecasts it to reach hurricane intensity in about three days.  As of Monday morning however, it is still embedded in dry air and strong wind shear.

Models are in excellent agreement on the storm passing well north of the Leeward Islands, then recurving by about 65°-70°W (the NHC forecast track follows the model consensus).  The primary concern then becomes Bermuda... Karl could reach Bermuda as a hurricane by Saturday.  The last hurricanes to pass over or close to Bermuda were Joaquin in October 2015 and then Fay and Gonzalo in October 2014 -- only 6 days apart from each other.

Invest 96L is very close to becoming Tropical Depression 13 or even Tropical Storm Lisa... probably later today.  Other recent years that had the 12th named storm form so early in the season are 2012, 2011, 2005, and 1995; all very active years (climatologically, there are only 7 by this date).

In the medium-long range, it does not appear that this system will be a threat... most models do not develop it much after this week, and they indicate that it will turn northward into the central Atlantic.

16 September 2016

Atlantic now has three named storms for first time in four years

Ian, Julia, and Karl are all tropical storms now, a level of activity not seen in the Atlantic since 2012 when Isaac, Kirk, and Leslie were all active. However, it will be hard to touch the record of four simultaneous hurricanes in the Atlantic: Georges, Ivan, Jeanne, and Karl in 1998 (note that Georges, Ivan, and Jeanne have since been retired).

Infrared satellite image of the Atlantic basin on Friday morning. (CIMSS)
Contrary to model guidance, nature decided that Julia was not finished yet, and it was re-upgraded to a tropical storm on Thursday afternoon.  The official forecast still calls for it to weaken and remain nearly stationary though, so it is not expected to become a threat to land.

Ian is still clinging onto tropical cyclone status, though barely.  This is the last you'll hear about it, but it did hang around long enough to assist with the "three simultaneous named storms" statistic!

And last but not least, Tropical Depression 12 was upgraded to Tropical Storm Karl, the 11th named storm of the season.  In an average season, the 11th named storm forms on October 28!  But as before, the overall activity as measured by ACE (Accumulated Cyclone Energy) is still lagging behind... roughly 74% of average for this date.  In other words, the season has had a lot of weak storms: they get named but don't get very strong or last for very long.

Karl is expected to remain relatively weak for the next several days, but by the middle of next week it could be in a position to intensify as it heads west. This graphic below shows a three-day forecast of the surface pressure and mid-level humidity -- Karl is the low pressure near 47°W surrounded by dry air (the next easterly wave behind it may also get named next week... it would be Lisa).

 In the longer range, most models still agree that it will get stronger and track toward the west-northwest.  It's too early to say if it will recurve toward Bermuda or keep a heading more toward the U.S.  Shown here is a plot of track forecasts from the GFS ensemble (a global dynamical model run multiple times with slightly different initial conditions to simulate uncertainty).  The lines are colored by intensity.  At this point, the majority have it recurving before it reaches 70°W, but that can change.

15 September 2016

Julia, Ian, and TD12 are scattered across the Atlantic

Today's update will be brief, as very little has changed since yesterday.

Surface wind field showing the circulations of the three active tropical cyclones in the Atlantic. (earth.nullschool.net)
Julia did eventually drift offshore after I wrote yesterday's post, and it also weakened to a tropical depression. It is expected to dissipate this weekend, but should remain virtually stationary the entire time due to a lack of steering flow.  This morning it is centered 85 miles east of the SC/GA border, with the "business end" (heavy rain, and thunderstorms, and strongest winds) displaced to the east of the center and away from land.

Sunrise over Tropical Depression Julia on Thursday morning.
Ian is still a moderate tropical storm with 50 mph peak winds, but remains embedded in a high-shear environment. The center is about 750 miles south-southeast of Newfoundland, but as you can see in the satellite image below, a frontal boundary is forming to its south, a tell-tale sign that it is transitioning to an extratropical cyclone.  NHC will likely cease writing advisories on it today or tomorrow.

And finally, Tropical Depression 12 is still forecast to battle with dry air for the next few days, but probably have a shot at intensification next week.  Should it reach tropical storm status, the next name on the list is Karl. It's presently not looking very ominous... just a low-level swirl with some widely scattered thunderstorm activity to its south.

The long-range forecasts are worth paying some attention to, at least to start watching for trends and consistency.  The plot below shows track forecasts from a variety of dynamical models out to 5-7 days, as well as the NHC forecast (black line).  There is general agreement that it will continue its westward motion and reach the area north of the Leeward Islands by late next week.  It is far too early to say anything certain about the intensity at that time, but for what it's worth, today's model runs indicate it would not be a hurricane at that point.

Stay tuned!

14 September 2016

Julia forms over Florida, Ian still a tropical storm, TD12 forms over Cabo Verde Islands

The peak of hurricane season isn't failing this year.  There are two active tropical storms, and a new tropical depression off the coast of Africa.

The tenth named storm of the season, Julia, formed near Jacksonville FL on Tuesday night.  It actually formed over land, and the center has not spent any time over water, and probably never will.  This is extraordinary, and from what I can tell, unprecedented.  While there are a dozen examples of Atlantic tropical cyclones forming inland near a coastline (Agnes 1972 over the Yucatan Peninsula, Leslie 2000 over northern Florida are two examples), they did eventually track over water and strengthen. Julia can be traced back to an easterly wave that left the African coast on September 1st.

Tropical Storm Julia on Wednesday morning.  Previous center locations are marked with red dots.
Julia is expected to weaken to a depression later today over South Carolina... the primary threat is heavy rainfall, and parts of eastern SC could receive 6-10" of rain over the next few days as it crawls northward.

During an average season (using a 1981-2010 climatology), the 10th named storm forms on October 10th, so this season is now about 3.5 weeks ahead by that measure.  But in terms of ACE (Accumulated Cyclone Energy), the season is still at roughly 73% of average for this date.

In the far eastern Atlantic, over the Cabo Verde Islands, Tropical Depression 12 has formed and could get named in the next day or two.  The next name on the list is Karl, a name that was on one of the original six lists of names in 1980.

Models strongly favor this depression to develop to at least a tropical storm, and they also agree on a track toward the west over the next 5 days.  On this general trajectory, the system would reach the Lesser Antilles by late next week. But it will likely struggle with wind shear and dry air for the next three or so days.

A selection of global and regional dynamical model forecast tracks for TD12, valid out through Monday morning.
Finally, as expected, Tropical Storm Ian has not intensified, and is embedded in strong vertical wind shear in the middle of the Atlantic.  It is no threat to land, and is forecast to transition to an extratropical cyclone by the weekend.

Visible satellite image of Tropical Storm Ian on Wednesday morning.
Forecast track of Ian over the next five days. (NOAA/NHC)

12 September 2016

Ian, season's ninth named storm, forms in central Atlantic

A tropical wave we've been tracking since it left the African coast on September 6th was upgraded to Tropical Storm Ian on Monday morning.  It is in the central Atlantic, nearly 600 miles east of the Leeward Islands and not forecast to affect land at any point.  This is the first use of the name Ian -- it replaces Igor from 2010 which was retired due to its severe impact in Newfoundland.

As the satellite image above shows, it is in an area of strong vertical wind shear... in this enhancement, the low-level clouds show up in the yellow shades, while the upper-level clouds are white.  The surface center of circulation is completely exposed.  It is a minimal tropical storm now (40mph maximum winds), and is forecast to strengthen just slightly as it heads north, then gradually transition to an extratropical cyclone by the weekend.

There are weather satellites in orbit than routinely measure the surface winds over water, they are called scatterometers. One such satellite passed right over Ian this morning and helped justify the upgrade to a tropical storm.  In this swath of wind vectors, the center is found toward the bottom, with winds circling counter-clockwise around it.

Climatologically, the 8th named storm forms on September 21, so this is a bit ahead of an "average" year (using a 1981-2010 climatology).  If you missed my post about the various climatologies, check out When is the ‘peak’ of hurricane season? It’s more complicated than you think.

However, in terms of ACE, this season is slipping behind, now at about 76% of average for this date.

02 September 2016

Hermine hit Florida as a hurricane, now a huge concern for northeast US coast

Today's update is a combination of posts.  The first, summarizing Hermine's landfall on Florida, is available on the Capital Weather Gang blog at:

Tropical Storm Hermine is headed up the East Coast after bruising northern Florida

Radar image from Tallahassee of Hurricane Hermine near the time of landfall, around 1:30 am.
Visible satellite image of Hermine as of midday Friday.
Not included in that post are some interesting and useful graphs pertaining to storm surge.
Unfortunately, Hermine’s peak storm surge coincided with high tide and created a water level that was 4.7 feet above the “highest astronomical tide” and six feet above the average high tide level.

It was the fifth highest water level ever observed in Cedar Key — the highest in 23 years. The only hurricane to generate a higher water level in the past century was Alma in 1966.

Timeline of surge events in Cedar Key.  (u-surge, Hal Needham)
The second part of the update on Hermine, which includes significant coastal impacts expected in the northeast U.S. (prolonged period of coastal erosion and flooding), was written by Capital Weather Gang's Jason Samenow:

Hermine to wallop Mid-Atlantic beaches, serious coastal flooding possible

I have a very long regional radar loop of Hermine available HERE ... please be patient, it may take a while to load.

Elsewhere, Gaston is still out there, now as a tropical storm.  It is over the Azores islands, which were also hit by Hurricane Alex in January. Gaston will continue to rapidly decay over cooler water, so this will likely be the last mention of it.

Tropical Storm Gaston.

01 September 2016

Hermine likely to rock Mid-Atlantic beaches with wind, rain and angry seas

Here is the promised Part 2 of today's update on Hermine.  The storm is very close to hurricane intensity now, and it appears likely that it will indeed make landfall as a hurricane tonight.  This post was written by Capital Weather Gang's Jason Samenow:

Hermine likely to rock Mid-Atlantic beaches with wind, rain and angry seas

Hermine could end Florida's 10.9-year hurricane drought tonight

This is the first part of the update on Tropical Storm Hermine.  I will send out a second post later that covers the portion of the forecast and impacts beyond Florida.

A hurricane hasn’t made Florida landfall in over 10 years. Hermine may end that streak.