28 September 2012

Nadine back up to hurricane intensity

Today's update actually focuses more on a noteworthy storm in the West Pacific ocean (Typhoon Jelawat), but also provides the latest on re-upgraded Hurricane Nadine.

The update can be found on the Washington Post's Capital Weather Gang blog.  As always, I appreciate your continued interest!

24 September 2012

Zombie storm haunts the north Atlantic

An easterly wave that exited the African coast on September 7 became TD14 on September 11.  It was upgraded to Tropical Storm Nadine just twelve hours later, and then Hurricane Nadine on September 15.  The "final" advisory was written on it this past Friday night, but 36 hours later, it came back from the graveyard, and is now a tropical storm again, and may become a hurricane... again.  So, as I mentioned a week ago, we'd still be talking about Nadine for quite some time!

At 09Z today (5am EDT), Nadine's estimated intensity was 45kts, and forecast to slowly intensify to a 65kt hurricane by the end of the week as it drifts westward.  In the image shown here, you can see the Azores to the north of the storm (yellow outlines) and an underwhelming satellite appearance.

Aside from Nadine, the basin is quiet, which is extremely fortunate because the primary "eye in the sky" failed on Sunday afternoon.  I'm referring to GOES-13, NOAA's operational geostationary satellite that provides continuous satellite images over the eastern US and Atlantic basin.  The satellite was launched in 2006, and was held in reserve until its predecessor failed in 2010.  So it's only been in operation for 2 years... not a good record.  It's possible that it can be fixed, but it would need to be by clever electrical engineers on the ground, since physically repairing it is not an option.  There is a spare satellite parked in orbit for exactly this scenario (GOES-14), but before pulling it out of storage, GOES-15 (the western operational satellite) will be used in full-disk mode to provide some coverage.  The GOES-15 view of the basin looks like this:

These geostationary satellites (named that because the satellite orbits the earth at the same rate the earth rotates, so it's always looking down at the exact same spot on the globe) must orbit at an altitude of 22,236 miles above the Earth's surface at the equator.

19 September 2012

Tropical storm conditions continue in the Azores

As expected, Tropical Storm Nadine has virtually stalled near the Azores, and isn't planning on moving out any time soon.  The enhanced satellite image below shows the high clouds associated with outflow or thunderstorms in white, while low shallow clouds appear yellow, and the ocean is dark blue.  The Azores islands are the purple outlines northeast of the storm's center.

[The Azores is an archipelago comprised of nine volcanic islands.  Six hundred years ago, these islands were uninhabited, but now are home to a quarter of a million Portuguese residents.  ]

At 09Z today, Nadine had 45kt maximum sustained winds with a 993mb central pressure.  It's crawling north at 4kts, and is forecast to gradually drift eastward over the next 5 days... leaving the Azores exposed to tropical storm conditions for around a week.  Luckily, it's not very intense, and there's limited rainfall on the eastern side lately.  But the 26' waves being reported at Santa Cruz (western part of the islands) are impressive.

As far as HS3 is concerned (NASA's big field program: Hurricane and Severe Storm Sentinel), today is a huge media day at Wallops Island where the unmanned aircraft is based.  The Global Hawk is scheduled to depart around 2pm EDT today for a 26-hour flight over Nadine, releasing 79 dropsondes over and around the storm in a "lawnmower pattern" to survey the environment.  The proposed flight path is shown here for reference.

The Azores is no stranger to tropical cyclone encounters.  They're in a fairly common path for recurving storms, and they don't always just get the "leftovers"... some encounters have been with potent hurricanes.  This map shows the tracks of the 23 storms that have passed directly over the Azores in the past 160 years.  In order to count, the center of the storm had to pass within 230 miles of the middle of the Azores and be at least a tropical or subtropical storm (depressions and extratropical systems aren't included).  Now the map will include Nadine!

Elsewhere, the basin is quiet during this climatologically active week.

17 September 2012

Nadine heading for the Azores

Over the weekend (03Z on Saturday), Nadine reached an intensity of 70kts, making it the season's 8th hurricane.  After a couple days, it weakened back to a tropical storm, but just barely.  At 15Z today, it's a 60kt tropical storm (at 65kt, it would be a hurricane, so it's a fine line between two different classifications) and heading ENE at 15kt toward the Azores islands.  In the image shown here, shallow clouds appear yellow, while deeper clouds (tops of thunderstorms or outflow) appear white.  From this, it's evident that the storm is becoming asymmetric and losing its centralized deep convection.

Models agree that a significant slow-down should occur, and in five days, we'll still be talking about Nadine near the Azores!  In fact, most guidance is showing a re-recurvature when Nadine reaches the Azores... coming back toward the southwest and possibly re-intensifying.  Recall that the first advisory was issued for Nadine (TD14 then) on the morning of September 11, and the last could still be at least a week away!

The official track forecast from NHC has the storm centered over the Azores in 5 days... as a tropical storm.

Elsewhere, the basin is abnormally quiet for mid-September.

In terms of ACE, the season has slipped to 134% of average for this date.  As I mentioned on Friday, every day without a hurricane (or major hurricane, or multiple hurricanes) this time of year is "behind" an average day.

14 September 2012

Nadine recurving as Global Hawk surveys its environment

Nadine has been on the TS-hurricane threshold (60kts) for about 36 hours now, and probably won't change much in the coming days as it recurves to the north and begins its extratropical transition. 

Track guidance is in good agreement on a path toward the Azores in about 6 days, perhaps as a hurricane, perhaps as a tropical storm, or perhaps as a potent extratropical storm (somewhere in the 50-70kt ballpark by the time it reaches the islands).  The NHC 5-day forecast is shown by the thick green line, while various models are shown by the thin multi-colored lines.  The Azores islands are labeled for reference.

The big NASA field program, HS3, is sending the Global Hawk unmanned aircraft to survey Nadine today, releasing 69 dropsondes in a 15x15 degree "lawnmower pattern" around the storm to get a detailed picture of the near-storm environment.  The state-of-the-art plane took off from Wallops at 10:00am EDT this morning, and will fly over Nadine until tomorrow morning at 6:15am.

Aside from Nadine, the basin is amazingly quiet for the second week of September.  There is an easterly wave centered right on the African coast that some global models (e.g. GFS and FIM) develop ever so slightly, while the others show it doing nothing.  We certainly have time to watch it and see if it's worth another mention.

The ACE (Accumulated Cyclone Energy) stands at 80.6 as of this morning, which is about 139% of what an average season would be at on this date.  This time of year, every day without a hurricane (or multiple hurricanes for that matter) lets 2012's ACE loose ground against the average because climatologically, ACE racks up real fast in mid-September.  We're very close to the ACE we had in 2010 and 2011 on this date.

12 September 2012

Nadine forms and becomes season's 14th named storm

At 03Z today (11pm EDT Tuesday night), TD14 was upgraded to TS Nadine.  It's quite extraordinary to have the 14th named storm occur on September 12th!!  As I mentioned a couple of days ago, I was only able to find two other years in 160 years of record-keeping in which the 14th storm formed sooner: 1936 and 2011.  I'm going to include a far-view satellite image as well as a full-resolution image (1km) from GOES-East... just because they're so pretty!

At 15Z today, Tropical Storm Nadine's maximum sustained winds are at 50kts, and it's most decidedly on an intensifying trend.  The NHC forecast brings it up to a hurricane (the season's 8th) by Thursday morning.
The track model guidance continues to be very closely bundled, and shows a recurvature by the time it reaches 55W, keeping it safely away from any land encounters.  Although it is in a healthy environment now, its time is limited, as strong vertical shear is in its future.

The graph below shows the forecasts of intensity, track, shear, SST, and mid-level humidity from a few key models.  You can see the expected intensification in the near future, but then the dramatically increasing shear, the decreasing SST, and the decreasing RH... all working together to keep Nadine from becoming an extremely intense hurricane.

This storm is also being throughly probed by unmanned aircraft as part of NASA's huge field program called "Hurricane and Severe Storm Sentinel", or HS3.  A centerpiece of the program is the Global Hawk, a highly advanced unmanned aircraft capable of flying very long missions, and it carries with it a large suite of instruments and dropsondes to send high-resolution enviromental data into operational computer models.  Check on the Capital Weather Gang's blog later for a more detailed description of this program and its activities with Nadine!

10 September 2012

Peak of season comes with Hurricane Michael, TS Leslie, and almost-TD14

Today is the climatological peak of the Atlantic hurricane season.  On average, this is the date when you're most likely to have tropical cyclone activity, and 2012 is no exception.  In fact, we nearly have one of each flavor!  We're extremely close to having Tropical Depression 14 in the eastern Atlantic, Tropical Storm Leslie north of Bemuda, and Hurricane Michael west of the Azores.

In this graph, the red curve represents tropical storm activity, while the yellow is for hurricanes.  There are still 81 days left in the official hurricane season, which ends on Nov 30.

Group photo of Leslie, Michael, and TD14-to-be.


Leslie never did reintensify to a hurricane, and passed 150 miles east of Bermuda on midday Sunday as a strong tropical storm.  The strongest sustained wind I could find on Bermuda was 34kts, with gusts to 47kts.  I'm including a radar image from when Leslie was at its closest approach.  The full long loop can be found here.

It is now on its way toward Canada... a hurricane watch and tropical storm warning have been issued for eastern Newfoundland. 


Michael has very slowly weakened, but is still hanging onto hurricane status.  It's a 70kt Category 1 storm now, and is forecast to become extratropical by Wednesday.  It has been a hurricane for four days now, which isn't bad considering its dismal extratropical origins.  It's presently about 1100 miles west of the Azores and heading W at 7kts.


The easterly wave that exited Africa on the 6th did indeed get organized in a hurry, as models predicted.  It will soon become TD14, and is located about 1500 miles east of the Lesser Antilles.

Models are in excellent agreement on the track, and show it heading WNW for the next couple days, then recurving by the time it reaches about 55W (a track in between Kirk's and Leslie's).  They also agree on this becoming TS Nadine very soon, then a hurricane in 3-4 days.  It will not be a threat to land.


In terms of ACE (Accumulated Cyclone Energy), we're now at 78.6 compared to the climatological value of 49.6 for this date... that's 158% of average!  And, we're going to soon see the 14th named storm this week, which is also quite amazing.  Only about 10% of years ever reach the 14th named storm, and this year, that should be accomplished this week.  The only years that I could find that beat this date for formation of the 14th named storm were 1936 (Sep 10th) and 2011 (Sep 7th).

08 September 2012

As Leslie and Michael head north, new disturbance brews off Africa

 Leslie remains a strong tropical storm, but appears to be on an upward swing today.  It has finally started moving, and is now roughly 250 miles southeast of Bermuda and heading north at 7kts.

With the increased forward speed, it also finally crept into better radar range from Bermuda.  I have a long radar loop available that will continue to add frames as the storm approaches and passes about 160 miles east of the island midday on Sunday (click here). The outer rainbands are already in range, and the developing eyewall should be in range shortly.

After passing by Bermuda tomorrow, it has a 3-day journey to get up to Newfoundland for its next close encounter, then could potentially interact with Michael prior to becoming an extratropical cyclone over the cold northern Atlantic Ocean.  A tropical storm warning is in effect for Bermuda.

Michael has made a bit of a comeback in its satellite presentation today, and remains a 90kt Category 2 hurricane.  Yesterday, the eye filled, the outflow was more asymmetric, and the circulation appeared more elliptical rather than circular, but today it looks a bit healthier... temporarily.

Hurricane Michael is 1100 miles southeast of Newfoundland, and is forecast to gradually weaken as it heads N-NW toward Newfoundland over the next few days.  Again, it will be interesting to see if any sort of binary vortex interaction (Fujiwhara effect) takes place with Leslie and Michael, but it would be on Tuesday-Wednesday, so we have time to keep an eye on that. 

And finally, to the disturbance off the coast of Africa that I mentioned the past couple of days.  The wave has an embedded 1008mb Low centered over the southern Cape Verde islands.  Models continue to be very bullish on this system, bringing it up to a hurricane in 4-5 days.  That may be a little too aggressive, but at any rate, models also agree on it recurving by the time it reaches 50-55W... far from affecting land.  The biggest factor working against it now is the dry Saharan Air Layer to its north, which you can see on this image as the milky air streaming off the continent (you're actually seeing tons of suspended fine dust acting as tracers in the dry air).  The next name on the list is Nadine.

07 September 2012

Special edition on the Saffir-Simpson Scale

I had the opportunity to weigh in on the usefulness and limitations of the well-known Saffir-Simpson Hurricane Wind Speed Scale, and thought I'd share the article with you.  Enjoy!

Leslie making waves along US east coast, Michael weakening

First, a quick mention of the "ghost of Isaac" that was brewing in the northern Gulf of Mexico.  Its window of opportunity to develop has closed... before it took advantage of it.  Conditions are now too unfavorable for genesis, and all that remains is a low-level swirl completely dislocated from what little thunderstorm activity there is.

On to Leslie... a tropical storm watch has been issued for Bermuda, but Hurricane Leslie is in no hurry to get there.  It has remained essentially stationary for the past four days, and MAYBE by Sunday it will start the long-awaited northward trek toward Bermuda and then Newfoundland.  It is a very sloppy 65kt storm now, and after sitting in the same place for so long, has likely upwelled a decent amount of cool water from the ocean depths. 

A long radar loop from Bermuda will help keep tabs on exactly where the center is, and provide constant surveillance of the inner core structure.  Although the center of the storm is currently 1100 miles east of the Florida peninsula, large swells and waves will affect the US east coast from North Carolina up to Maine in the coming days.  Shown here is the wave height forecast valid on Tuesday (wave heights are in meters... multiply by 3.3 to get approximate conversion to feet).  Definitely a concern for boating interests, and for rip currents on the beaches.

Michael has weakened just slightly to a 90kt Category 2 hurricane as of 09Z this morning.  It is forecast to continue the gradual weakening as it heads north into the cold north-central Atlantic.  It's presently located about 900 miles WSW of the Azores and drifting north at 3kts.

Finally, a strong easterly wave left the African coast yesterday, and has an embedded 1007-1008mb Low.  This disturbance is favored by all of the global models to develop rather quickly in the coming days as it heads WNW -- and will likely become Nadine next week.

04 September 2012

Watching tropical storms Leslie and Michael

Over the long weekend, Kirk made the anticipated recurvature at 51W, and then headed northeast into the cold north-central Atlantic hurricane graveyard.  The final advisory was written on Sunday morning as the storm became an extratropical cyclone.

Now on to Leslie and Michael...

Leslie is still a tropical storm, having encountered much stronger vertical shear than expected.  This morning, the storm is remains lopsided, and conditions are not expected to improve until closer to the weekend when it's forecast to become a hurricane.  The forecast track is far away from land... it's currently about 870 miles east of the northern Bahamas and 420 miles north of the Virgin Islands, and crawling northward.

Elsewhere, Tropical Depression 13 formed from an upper-level Low on Monday evening in nearly the place that Kirk formed.  Although it is also rather lopsided and extremely tiny, there are several ships as well as satellite data to support the recent upgrade to Tropical Storm Michael.  Getting the 13th named storm on September 4 is absolutely remarkable.  It's ahead of 1933 and 2004, and just 2 days behind the unprecedented 2005 season (when we needed to borrow six names from the Greek alphabet).  Michael is located about 1400 miles ESE of Bermuda, and about 1300 miles SW of the Azores... truly in the middle of the ocean.  The guidance suggests that it will slowly meander northward and remain a disorganized tropical storm for the next few days  -- no threat to land.