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99L and 90L May Soon Develop in Atlantic; Fiona Clings to Life

By: Jeff Masters and Bob Henson 4:28 PM GMT on August 21, 2016

A large but nearly thunderstorm-free tropical wave (Invest 99L) was located in the tropical Atlantic about 1100 miles east of the Lesser Antilles Islands late Sunday morning, and was headed west at 15 - 20 mph. This disturbance is not likely to develop into a tropical depression or tropical storm before moving into the Lesser Antilles Islands on Tuesday night, but will bring some heavy rains and gusty winds to the islands on Tuesday and Wednesday. The storm could be a long-range threat to the U.S. East Coast from Florida northwards in about 7 - 10 days.

The most impressive thing about 99L when viewing satellite loops is its very large size and excellent spin. A large region of the atmosphere has been put in motion by this disturbance, which is both good news and bad news: good news because such large disturbances typically take a long time to spin up into a tropical cyclone, but bad news because once they do, they affect a large area and will resist rapid weakening. The other notable feature of the storm on Sunday morning was the lack of heavy thunderstorm activity, due to dry air from the Saharan Air Layer (SAL), as seen in water vapor satellite imagery. However, this dry air was only moderately dry, with humidities at mid-levels of the atmosphere between 500 - 700 mb running about 60%, and the circulation of 99L was getting more defined late Sunday morning, potentially signaling that the storm might be about to build some heavy thunderstorms near its center. Other conditions were generally favorable for development, with wind shear a moderate 10 - 15 knots and sea surface temperatures (SSTs) near 27.5°C (82°F), which was close to average. 


Figure 1. Latest satellite image of 99L.

Track forecast: 99L a potential threat to Hispaniola, the Bahamas, and the U.S. coast from Florida northwards
A strong ridge of high pressure will keep 99L headed north of due west over the next few days, and the storm should pass through the northern Lesser Antilles Tuesday night through Wednesday, track close to Puerto Rico on Wednesday night, and affect Hispaniola and the Southeastern Bahamas by Thursday. The uncertainty about the track increases greatly thereafter, as a weak trough of low pressure passing to the north of 99L late this week may be strong enough to turn the storm to the north before it can reach the U.S. East Coast. The track of 99L may also be affected late this week by tropical wave 90L (see below), which could grow into a hurricane that comes close enough to exert a steering influence.


Figure 2. The dry air of the Saharan Air Layer (SAL) as analyzed by satellite at 8 am EDT Sunday, August 21, 2016. The SAL was interfering with both Fiona and 99L, but was not as concentrated as we saw early in August. Image credit: University of Wisconsin CIMSS/NOAA Hurricane Research Division.

Intensity forecast for 99L
99L has a lot of hurdles to overcome to become a named storm. The 8 am EDT Sunday run of the SHIPS model showed moderately favorable conditions for development through Thursday, with wind shear in the moderate range, 10 - 15 knots, a relatively moist atmosphere, and SSTs near 28°C (83°F.) The total heat content of the ocean will steadily increase as 99L moves westwards, as well. But working against development of 99L will be the large size of the storm, dry air of the SAL, potential interaction with the land areas of Puerto Rico and Hispaniola, and large scale sinking air over the tropical Atlantic imparted by an unfavorable phase of the Madden-Julian Oscillation (MJO). The active portion of the MJO is currently located in the Western Pacific, which is leading to increased tropical cyclone activity there--three named storms were active there on Sunday morning. This positioning of the MJO typically leads to compensating sinking air and surface high pressure over the tropical Atlantic, with reduced chances of tropical cyclone development there.

None of the Sunday morning (00Z) operational runs of our three reliable models for predicting tropical cyclone genesis--the European, GFS and UKMET models--showed development of 99L into a tropical depression or tropical storm over the next five days. However, beyond five days, when the storm will likely be near or just north of the central Bahamas, the models are predicting a more favorable environment for development. The 00Z Sunday runs of the GFS and European model ensembles had 5% and 12% of their members predicting that 99L would eventually become a hurricane, after seven days. In their 8 am EDT Sunday Tropical Weather Outlook, NHC gave 99L 2-day and 5-day development odds of 20% and 50%, respectively.


Figure 3. MODIS visible satellite image of 90L off the coast of Africa, taken on Sunday morning, August 21, 2016. Image credit: NASA.

90L off the coast of Africa likely to develop
A large tropical wave with plenty of spin (Invest 90L) emerged from the coast of Africa on Saturday night, and appears poised to become a tropical depression by Tuesday as it heads west-northwest at about 10 mph. Satellite images on Sunday morning showed that 90L was well-organized, with low-level spiral bands and an increasing amount of heavy thunderstorms. Wind shear was light, 5 -10 knots, and SSTs were warm enough for development, 27°C (81°F).

The Sunday morning operational runs of the European, GFS and UKMET models all showed development of this wave into a tropical depression in 1 - 3 days. In their 8 am EDT Sunday Tropical Weather Outlook, NHC gave this disturbance 2-day and 5-day development odds of 70% and 90%, respectively. The wave will head west-northwest through Tuesday, skirting the Cabo Verde Islands to the south, then turn more to the northwest on a path similar to Fiona’s. The storm will be moving into a region of ocean where very few tropical cyclones ever make the long trek westwards to hit the United States--though 90L could be a long-range threat to Bermuda. The next name on the list of Atlantic storms is Gaston, and we can expect 90L to be called Hurricane Gaston by this weekend.


Figure 4. With its shell of convection displaced far to its east by strong vertical wind shear, Tropical Storm Fiona’s low-level center was left completely exposed (left) at 0745Z (3:45 am EDT) Sunday, August 21, 2016. Less than seven hours later, at 1415Z (10:15 am EDT), a new burst of convection had developed near Fiona’s center (right). Image credit: NOAA/NESDIS.

Fiona the fighter lives to see another day
The epitaph was almost written Saturday night on Tropical Storm Fiona. The storm had intensified Saturday afternoon, with a substantial core of convection helping the storm’s top sustained winds to increase to 50 mph as measured by scatterometer. Overnight, though, strong wind shear (around 30 knots) ripped away the convection and left Fiona’s low-level circulation completely open. Early Sunday morning, yet another burst of convection erupted near Fiona’s center. Fiona’s small size and the typical overnight maximum in tropical convection are helping to facilitate these ups and downs in intensity. As of 11 am EDT Sunday, Fiona’s top winds were 40 mph, barely keeping it a tropical storm. Working its way across the open Atlantic, at 22.9°N, 53.3°W--roughly 700 miles northeast of the Leeward Islands--Fiona was continuing west-northwest at 16 mph.

The main question in Fiona’s future is whether the storm will survive the 20-30 knot wind shear projected for the next 1-2 days. After that point, wind shear will drop below 20 knots, and the storm will be traveling over very warm SSTs of around 30°C (86°F), around 1-2°C above average for this time of year. The contrast between these warm waters and cold upper-level temperatures in the subtropics would allow for strong convection, and Fiona’s small size could allow the storm to intensify more quickly than a larger storm might. Recent runs of the European model weakens Fiona into an open trough, while the GFS, UKMET, and HWRF maintain it as a weak low through the 5-day forecast period. The official NHC outlook downgrades Fiona to depression strength by Monday and makes Fiona a remnant low by Tuesday. If Fiona does survive, it could become a respectably strong tropical storm late in the week, potentially passing near Bermuda on a recurving path north and northeast.

East Pacific: Tropical Storm Kay on the downswing
About 300 miles southwest of Cabo San Lucas, Tropical Storm Kay peaked at 50 mph sustained winds on Saturday. Although it’s a well-structured storm, Kay will continue weakening as it passes over progressively colder waters on its slow northwest track, most likely becoming a remnant low by Tuesday. There are no other systems of interest in the East Pacific for the next several days.


FIgure 5. Infrared image of Tropical Storm Kay as of 1500Z (11:00 am EDT) Sunday, August 21, 2016. Image credit: CSU/RAMMB/CIRA.


Figure 6. Satellite image early Sunday EDT of Tropical Storm Mindule (center of image), which was approaching the Tokyo area on Sunday. Tropical Storm Lionrock can be seen at lower left, while Tropical Depression Kompasu is off the image to the northeast.

Back-to-back tropical systems hitting Japan
The northern West Pacific has been bubbling with activity this weekend (see embedded video below), though none of the systems were at typhoon strength on Sunday. Tropical Depression Kompasu brushed eastern Japan on Sunday before dissipating. Kompasu produced heavy rains across Hokkaido, where flood and landslide alerts have been issued. On the island’s north coast, at least 3000 residents have been evacuated from the city of Kitami due to flooding, with 5” - 7” of rain reported across the area. Hard on the heels of Kompasu is Tropical Storm Mindule, with current sustained winds of 50 mph. Mindule is projected to make landfall near Tokyo on Monday before racing northeastward on a path similar to Kompasu’s, which will likely exacerbate flood conditions on Hokkaido.

The most offbeat of the bunch is Tropical Storm Lionrock, which has been tracking toward the southwest over the last three days, paralleling the coast of Japan about 200 miles offshore. Now located about 200 miles southeast of Kyushu, with top sustained winds of just 40 mph, Lionrock will continue drifting southwest for the next several days.

We’ll be back with our next update on Monday.

Jeff Masters and Bob Henson



Tropical

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

Starting to see some signs of a more vigorous lower level circulation slipping underneath the convective burst closer to the center axis in this loop:




1502. palmpt
Quoting 1499. George1938:

I feel as though 99L (if) it gets the name Hermine it will sound better in the news. Something sounds more threatening about it.

I'm not a big "gut feeling" guy, but I do have one of those on 99L... It's going to be Gaston.
Hello folks, ......
Quoting 1500. ProgressivePulse:



Also a good indicator of the ridging that will be in place, 99L may just absorb what's left of Fiona.


What? I thought it would curve out to sea. Guess FL will have too watch two systems now.
Quoting 1502. palmpt:


I'm not a big "gut feeling" guy, but I do have one of those on 99L... It's going to be Gaston.

No, 90L will be. 90L will likely be named TD 7 at the 5:00 pm advisory and Gaston by 11:00.
1506. Gearsts
New image showing more convection.
1508. hydrus
Quoting 1503. forecaster1:

Hello folks, ......
Greetings...u left us..:)
Hope Bob and Jeff know how appreciated we are to be a part of this blog. And how thankful we are for them to take the time to create such an amazing analysis and giving us a place for us to come share this common interest and it be PROTECTED by moderators.
Quoting 1506. Gearsts:

New image showing more convection.




It almost looks like it is trying to wrap itself up around 17N and 50W....
Through 96hrs over the SE Bahamas but is just a wave.

It's interesting that it tries to develop 99L until it crosses the Lesser Antilles then, it loses its area of low pressure which cause it to not develop and never develops despite favorable conditions over the Bahamas. We need some real time data into these models because it does make much sense.
gaston is march march closer too the USA this run still far out there





but am not llikeing the look at this
Of course now that 99L looks its best the GFS drops it within the 5 day window...

90L moving west.

Quoting 1504. birdsrock2016:



What? I thought it would curve out to sea. Guess FL will have too watch two systems now.


nope

Quoting 1353. tigerdeF:



Why is it troubling? It appears to be dissipating anyway.

It has appeared to dissipate away a few times already but this time should be its last.
Looks like GFS wont develop 99L this run lol
And ironic that the the first "dot" of concentrated convection closest to the eventual coc has just fired over the past few hours right at 50W - 17N...................Hello World.



Quoting 1511. Ricki13th:

Through 96hrs over the SE Bahamas but is just a wave.

It's interesting that it tries to develop 99L until it crosses the Lesser Antilles then, it loses its area of low pressure which cause it to not develop and never develops despite favorable conditions over the Bahamas. We need some real time data into these models because it does make much sense.


that's why I've been saying models are crap
we need recon flight models will become less crap once we get recon flights going so that data can go in models and fix them
the GFS i would say is a out liner now for 99L


the way 99L is looking we could see a TD or TS by time it makes it too the Lesser Antilles.
What if it's a tie. lol

Quoting 1505. NCHurricaneTracker69:


No, 90L will be. 90L will likely be named TD 7 at the 5:00 pm advisory and Gaston by 11:00.
1521. LargoFl
Updated 11:00 am CIMSS charts; nice vorticity at the surface, very weak mid level vort behind the surface vort (at this point), and tutt free all the way to PR:


Surface:



Mid:



Upper:
Don't leave us dry 99L.

Quoting 1517. weathermanwannabe:

And ironic that the the first "dot" of concentrated convection closest to the eventual coc has just fired over the past few hours right at 50W - 17N...................Hello World.




The HWRF run from this morning did show colder cloud tops like what we are seeing now with 99L. Perhaps, it is better to nowcast then forecast where this thing will go and how strong it will get, until we get better sampling of the atmosphere and data from the recon fed into these models.

Quoting 1520. HaoleboySurfEC:

What if it's a tie. lol




It goes to the base runner
Quoting 1517. weathermanwannabe:

And ironic that the the first "dot" of concentrated convection closest to the eventual coc has just fired over the past few hours right at 50W - 17N...................Hello World.






coc is more at 15.5N 50.3W imo

that spot at 17N50W is just apart of the larger Northern banding that is building imo
1528. Siker
UKMET strongest yet, further southwest:

NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 96 HOURS
FORECAST POSITION AT T+ 96 : 23.3N 72.7W

LEAD CENTRAL MAXIMUM WIND
VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS)
-------------- ---- -------- ------------- -------------
1200UTC 26.08.2016 96 23.3N 72.7W 1008 23
0000UTC 27.08.2016 108 24.5N 73.0W 1007 27
1200UTC 27.08.2016 120 25.6N 74.1W 1006 31
0000UTC 28.08.2016 132 26.4N 75.9W 1002 36
1200UTC 28.08.2016 144 26.6N 78.3W 996 43
Quoting 1525. GTstormChaserCaleb:

The HWRF run from this morning did show colder cloud tops like what we are seeing now with 99L. Perhaps, it is better to nowcast then forecast where this thing will go and how strong it will get, until we get better sampling of the atmosphere and data from the recon fed into these models.




Blog: One whole day? But I want recon now!
It appears to have a very nice window of opportunity to develop into a tropical depression over the next 36-48 hours IMHO; could be as early as tomorrow afternoon or as late as Wed and defy some of the current model outlooks if convection really blossoms tonight and pressures drop by tomorrow morning consolidating some of the large area:



Meanwhile, 99L is becoming better organized as the low level spin becomes better defined. I guess that means it's closer to develop now that the GFS has dropped it. If current trends continue we might have a TC by the time the HH go out tomorrow. I'm going big at the next TWO 50/70.
Best day of 2016 coming? :)
1533. ProPoly
Quoting 1496. wunderkidcayman:

yeah I think Fiona may just go into Florida if there is anything left of her whether its TD Fiona Rem Low Fiona or nothing Fiona it might go into Florida





Mode ridging.
man I wish we had recon flying in 99L today or early tomorrow morning instead of 15Z taking off 13Z tomorrow
Looks like Fiona is about to enter an area with low shear, we may have forgotten about her a little too soon.
Quoting 1531. Ricki13th:

Meanwhile, 99L is becoming better organized as the low level spin becomes better defined. I guess that means it's closer to develop now that the GFS has dropped it. If current trends continue we might have a TC by the time the HH go out tomorrow. I'm going big at the next TWO 50/70.


Hopefully it won't disappoint...
Quoting 1535. pipelines:

Looks like Fiona is about to enter an area with low shear, we may have forgotten about her a little too soon.



no Fiona is done
Quoting 1526. win1gamegiantsplease:



It goes to the base runner
That would mean 99L since it's on second base, 90L has only just left the batters box.
1539. hydrus
Quoting 1525. GTstormChaserCaleb:

The HWRF run from this morning did show colder cloud tops like what we are seeing now with 99L. Perhaps, it is better to nowcast then forecast where this thing will go and how strong it will get, until we get better sampling of the atmosphere and data from the recon fed into these models.


Do you have a link to that Caleb.?
Quoting 1537. thetwilightzone:



no Fiona is done


I disagree, the doc said once it entered low shear, if it was still together, it had a chance to strengthen. Well it's entering an area of low shear, it's still together (blowing up convection as we speak), so it appears it has a chance to strengthen.
Quoting 1519. thetwilightzone:

the GFS i would say is a out liner now for 99L


the way 99L is looking we could see a TD or TS by time it makes it too the Lesser Antilles.

I believe Dr. Masters said that this would form a few days ago
when it get's to the Lesser Antilles.... And all of us know that
the GFS drops storms then picks them back up when they do
form....
So part of the course and right on schedule.... j/s

Taco :o)
Not understanding why the models continue to keep this weak until the Bahamas. It almost seems like the GFS runs from a few days ago are starting to verify, or at least the HWRF forecast models. If this stays north of the islands, I don't see what can stop this from becoming a Hurricane before threatening the USA. Everybody on the East Coast and even the Gulf Coasts need to monitor the progress of this potential storm. We may be dealing with a TS for the islands in a few days.
12z GFS going out
Quoting 1540. pipelines:



I disagree, the doc said once it entered low shear, if it was still together, it had a chance to strengthen. Well it's entering an area of low shear, it's still together (blowing up convection as we speak), so it appears it has a chance to strengthen.


that what the DOC said the model are saying it will DISSIPATED

you need too read what the NHC says not what DR M says


TROPICAL DEPRESSION FIONA DISCUSSION NUMBER 23
NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016
1100 AM AST MON AUG 22 2016

The satellite depiction of Fiona currently features an exposed
low-level circulation with a few small areas of convection
southeast of the center. Subjective satellite intensity estimates
from TAFB and SAB are 30 kt, while the various objective estimates
range from 25-45 kt. The initial intensity remains 30 kt based
mainly on the subjective estimates.

The dynamical models forecast that the current westerly vertical
shear will subside somewhat by 48 hours as Fiona moves under an
upper-level trough into an area of easterly upper-level winds to
the north of the trough. By 72 hours, the models forecast the
cyclone or its remnants to encounter a second trough, which should
produce another round of strong southwesterly shear. Based on the
premise that the cyclone will not be able to respond to the brief
period of more favorable conditions, the new intensity forecast
calls for Fiona to gradually decay and become a remnant low in about
36 hours. This would be followed by the system weakening to a trough

after 96 hours.

The initial motion is 285/16. The guidance remains in good
agreement on the forecast track through 72 hours, with Fiona moving
west-northwestward to northwestward toward a developing break in
the subtropical ridge. Beyond that time, the guidance diverges,
with the ECMWF turning the remnants of the system northeastward
while the GFS and UKMET show a westward turn. The new forecast
track will compromise between these extremes in showing a slow
north-northwestward motion. The new forecast track is shifted a
little to the west of the previous track and lies near the various
consensus models.


FORECAST POSITIONS AND MAX WINDS

INIT 22/1500Z 24.6N 59.7W 30 KT 35 MPH
12H 23/0000Z 25.3N 61.5W 30 KT 35 MPH
24H 23/1200Z 26.1N 63.5W 30 KT 35 MPH
36H 24/0000Z 27.0N 65.2W 30 KT 35 MPH...POST-TROP/REMNT LOW
48H 24/1200Z 28.1N 66.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 25/1200Z 30.0N 68.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 26/1200Z 31.5N 68.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 27/1200Z...DISSIPATED
Quoting 1539. hydrus:

Do you have a link to that Caleb.?
Simulated IR4 Satellite
1546. Grothar
If you want the Doc to come on or Mr. Henson. I'll make a post. They usually come right on.

seeing an outflow boundary coming out of 99. likely no development until the bahamas 90 almost there
1548. beell
Counting last night into this morning, 99L has persistence. A slightly n/s elongated, closed low AOA 16N, 51W.
Ship it!
JeffMasters has created a new entry.
Quoting 1548. beell:

Counting last night into this morning, 99L has persistence. A slightly n/s elongated, closed low AOA 16N, 51W.
Ship it!


I was just looking at that :o)
thinking the samething..

Taco :o)
Hmm...still some drier air aloft?

Hmm even more interesting

Quoting 1491. jazzygal:



I believe it is up to 60,700 homes damaged or destroyed as of this morning.

It is actually in excess of 100k.
HWRF time.
Quoting 1517. weathermanwannabe:

And ironic that the the first "dot" of concentrated convection closest to the eventual coc has just fired over the past few hours right at 50W - 17N...................Hello World.





Td 8 forming forming with 99l , maybe ts Hermine by this evening.
Quoting 1512. thetwilightzone:

gaston is march march closer too the USA this run still far out there





but am not llikeing the look at this
You are the only poster who i don't need to look at the user name to know who it is! You thinking a conus hit at this point?
1558. aquak9
Quoting 1548. beell:
Counting last night into this morning, 99L has persistence. A slightly n/s elongated, closed low AOA 16N, 51W.
Ship it!


Ship it? Where? Charleston? Wilmington?

(looks at maps, tosses chicken feathers and goat bones)

oh crap....
1559. hydrus
Quoting 1556. Camille33:


Td 8 forming forming with 99l , maybe ts Hermine by this evening.
TD maybe..I believe 90L will be Gaston today, and tomorrow 99L Hermine...jmo..pfft
Quoting 1483. win1gamegiantsplease:



I was four or five years old when that word was created, I must be born in the middle ages ;p


Simpsons Season 7, Episode 16. Lisa the Iconoclast. "A noble spirit embiggens the smallest man."
1561. IDTH
Quoting 1531. Ricki13th:

Meanwhile, 99L is becoming better organized as the low level spin becomes better defined. I guess that means it's closer to develop now that the GFS has dropped it. If current trends continue we might have a TC by the time the HH go out tomorrow. I'm going big at the next TWO 50/70.

Story of the 2016 Hurricane Season so far.