ATL: KATIA - Post Tropical - Discussion

[Typhoon_Willie]

From the 11pm discussion...

THE INITIAL MOTION IS NOW 290/13 KT BASED ON A BLEND OF VISIBLE AND
MICROWAVE SATELLITE FIXES. THE GLOBAL AND REGIONAL MODELS ARE IN
EXCELLENT AGREEMENT ON A GENERAL WEST-NORTHWESTWARD MOTION OVER THE
NEXT 5 DAYS...BUT THERE ARE SPEED DIFFERENCES IN THE MODELS. THE
GFDL...UKMET...CANADIAN AND ECMWF MOVE THE DEPRESSION THE
FASTEST...WHEREAS THE GFS...HWRF...AND NOGAPS ARE SLOWER.
HOWEVER...THE TREND IN THE MOST RECENT MODEL RUNS HAS BEEN TO
WEAKEN THE MID/UPPER-LEVEL LOW NEAR 30N55W AND LIFT IT OUT TO THE
NORTHEAST SOONER THAN IN PREVIOUS RUNS. THIS RESULTS IN LESS OF A
WEAKNESS IN THE SUBTROPICAL RIDGE...WHICH IS ALSO FORECAST TO
CHANGE ITS CURRENT NORTH-SOUTH CONFIGURATION TO AN EAST-WEST
ORIENTATION BY 72 HOURS. THIS CHANGE IN THE STEERING FLOW SHOULD
KEEP THE CYCLONE MOVING ON A WEST-NORTHWESTWARD TRACK FOR THE NEXT
4 DAYS...AND THEN SLOW DOWN AND POSSIBLY TURN MORE WESTWARD BY DAY
5 AS A NARROW RIDGE DEVELOPS TO THE NORTH AND WEST OF THE SYSTEM.
SINCE THE DEPRESSION IS BASICALLY ON TRACK...THE NEW NHC FORECAST
IS JUST AN UPDATE AND EXTENSION OF THE PREVIOUS ADVISORY TRACK.

[LarryWx]

- I found 48 TC’s from the period 1960-2010 that had formed by 28W and which were located between 8-17N near the longitude where TD #12 was declared (26.3W). Of these 48, 10 (21%) went on to hit the CONUS.

- Of the other 38, 11 (23%) dissipated over the ocean prior to a recurve (the category often neglected in discussions), 27 (56%) recurved, and none moved into MX or C.A.

- Five of the ten hits were from TC’s near the 10-11N range, two were near 12-13N, and the other three were near 14N. So, all were within ~10-14 N. A respectable six of the 20 (30%) within the 8-12N range, where TD #12 was located, later hit the CONUS. So, the low lat. helps TD #12/Katia’s CONUS hit chances, which is intuitive.

- However, the hit chances are reduced substantially when considering TD #12’s heading between ~25 and 30W:

1) The range of headings for the 48 TC’s was from ~250 deg. (WSW) to ~315 deg. (NW). ALL ten hits were from TC’s with headings of ~260-280 deg.! There was only one TC of the 48 that was less than 260 (with it at ~250). I count 25 TC’s with headings of ~260-280 deg. So,a whopping 40% of the 25 TC’s with a 260-280 heading hit the CONUS! A respectable 8 of the 26 TC’s (31%) with headings within ~250-280 deg. dissipated. So, only 8 of the 26 (31%) with headings of 250-280 recurved.

2) OTOH, there were 22 TC’s within the ~281-315 deg. interval with 21 of these 22 within ~281-300. NONE of those 22 got any closer than ~500 miles from the CONUS or made it to 70W! (The closest was Luis of 1995.) That is in stark contrast to the 13 of the 25 in the 260-280 group making it at least to 70W. A whopping 19 of the 22 (86%) recurved, which is almost three times the % of those with headings of 250-280!

3) TD #12 is on a heading of ~290 deg. (WNW) per the 11 PM EDT 8/29 NHC advisory discussion. I count only seven of the 48 TC’s with headings of ~290+. The furthest west/closest to the CONUS any of these seven got was 65.9W/~700 miles (Igor of 2010).

4) Therefore, despite the low lat. of TD #12, I feel comfortable maintaining a high (say ~90%) chance that TD #12/Katia will not hit the CONUS, especially considering that the GFS/Euro still show/suggest a recurve due to a lack of sig. high pressure over the W Atl. If the lat. had not been so low, I may have already gone with ~95% chance of no hit. I will update my %’s over the days to come.

[locke]

Nice detailed post Larry. The reasoning seems sound but my only question would be whether the current heading is actually 290.

Looking at the current positioning on satellite. I very much doubt the system will be North of 12N by the time it reaches 35W where as the last forecast from NHC had it close to 13N when reaching 35W. It is already nearly outside of the southern side of the guidance envelope that NHC have posted.

I think when a system such as this one is in its formative stages and is being affected by shear you cant be entirely confident of its current movement direction. I suspect the movement has been closer to 270-280 in the past 12 hours but the circulation has been somewhat obscured.

I think things might be a little clearer in 24 hours. But i anticipate the track will shift significantly westwards in the next update.

[phwxenthusiast]

this is soon to be upgraded to TS Katia if FNMOC were to be believed...

[Kohlecane]

WELCOME KATIA

[southerngale]

BULLETIN
TROPICAL STORM KATIA ADVISORY NUMBER 5
NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011
500 AM AST TUE AUG 30 2011

...NEW TROPICAL STORM MOVING QUICKLY WEST-NORTHWESTWARD ACROSS THE
TROPICAL ATLANTIC...


SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...11.8N 31.7W
ABOUT 535 MI...855 KM WSW OF THE SOUTHERNMOST CAPE VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...1006 MB...29.71 INCHES


WATCHES AND WARNINGS
--------------------
THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 500 AM AST...0900 UTC...THE CENTER OF TROPICAL STORM KATIA WAS
LOCATED NEAR LATITUDE 11.8 NORTH...LONGITUDE 31.7 WEST. KATIA IS
MOVING TOWARD THE WEST-NORTHWEST NEAR 17 MPH...28 KM/H. THIS GENERAL
MOTION IS EXPECTED TO CONTINUE OVER THE NEXT 48 HOURS WITH A
GRADUAL INCREASE IN FORWARD SPEED.

MAXIMUM SUSTAINED WINDS HAVE INCREASED TO NEAR 40 MPH...65 KM/H...
WITH HIGHER GUSTS. ADDITIONAL STRENGTHENING IS FORECAST DURING
THE NEXT 48 HOURS...AND KATIA IS EXPECTED TO BE NEAR HURRICANE
INTENSITY BY LATE WEDNESDAY OR EARLY THURSDAY.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 35 MILES...55 KM
FROM THE CENTER.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 1006 MB...29.71 INCHES.


HAZARDS AFFECTING LAND
----------------------
NONE.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...1100 AM AST.

$$
FORECASTER BRENNAN



----------------------------------



TROPICAL STORM KATIA DISCUSSION NUMBER 5
NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011
500 AM AST TUE AUG 30 2011

THE CONVECTIVE PATTERN OF THE CYCLONE HAS IMPROVED OVERNIGHT...WITH
A LARGE AREA OF COLD CLOUD TOPS NOW SITUATED TO THE WEST AND
SOUTHWEST OF THE ESTIMATED CENTER LOCATION. THE 06Z DVORAK
INTENSITY ESTIMATES FROM TAFB AND SAB WERE BOTH 2.5/35 KT...AND ON
THIS BASIS THE CYCLONE IS UPGRADED TO A TROPICAL STORM. THE
STRUCTURE OF KATIA IS CONSISTENT WITH THE 15-20 KT OF
EAST-NORTHEASTERLY SHEAR OVER THE CYCLONE ANALYZED BY THE SHIPS
MODEL AND UW-CIMSS. THIS SHEAR SHOULD DECREASE IN THE NEXT 12 HOURS
OR SO...AND AFTER THAT TIME STEADY INTENSIFICATION SHOULD COMMENCE
AS THE CYCLONE MOVES OVER PROGRESSIVELY HIGHER OCEAN HEAT CONTENT.
MOST OF THE INTENSITY GUIDANCE HAS TRENDED UPWARD THIS CYCLE...AND
THE OFFICIAL FORECAST HAS AS WELL. KATIA IS EXPECTED TO BE NEAR
HURRICANE STRENGTH WITHIN 36 TO 48 HOURS WITH CONTINUED
STRENGTHENING TO NEAR MAJOR HURRICANE STATUS BY THE END OF THE
PERIOD. THE NHC FORECAST IS CLOSE TO THE MULTI-MODEL CONSENSUS THAT
INCLUDES THE HFIP INTENSITY AIDS.

A TIMELY AMSR-E PASS FROM 0326Z WAS HELPFUL IN LOCATING THE CENTER
ON THE EASTERN EDGE OF THE DEEP CONVECTION...WHICH WAS A BIT NORTH
OF PREVIOUS ESTIMATES. THE INITIAL MOTION ESTIMATE IS 290/15...AS
KATIA CONTINUES TO BE STEERED WEST-NORTHWESTWARD BY THE SUBTROPICAL
RIDGE TO ITS NORTH. THE MODEL GUIDANCE IS IN GOOD AGREEMENT ON A
CONTINUATION OF THIS GENERAL MOTION THROUGH THE PERIOD AS THE
MID-LEVEL RIDGE BUILDS WESTWARD TO THE NORTH OF THE CYCLONE. AT
DAYS 4 AND 5...THE WESTERN EDGE OF THE RIDGE BEGINS TO WEAKEN AS A
MID-LEVEL TROUGH AMPLIFIES OVER THE WESTERN ATLANTIC...WHICH SHOULD
RESULT IN SOME DECREASE IN FORWARD SPEED. THE TRACK GUIDANCE
REMAINS TIGHTLY CLUSTERED BUT THERE ARE SOME FORWARD SPEED
DIFFERENCES...WITH THE UKMET AND GFDL MODELS ON THE FAST SIDE OF
THE GUIDANCE AND THE GFS CONTINUING TO BE A SLOW OUTLIER. FOR THIS
CYCLE THE MODELS HAVE TRENDED FASTER DURING THE FIRST 72 HOURS...
AND SO HAS THE OFFICIAL FORECAST. OTHERWISE...THE NHC FORECAST IS
VERY CLOSE TO THE PREVIOUS ONE AND LIES NEAR OR A LITTLE TO THE
RIGHT OF THE TVCA MULTI-MODEL CONSENSUS THROUGH THE PERIOD.


FORECAST POSITIONS AND MAX WINDS

INIT 30/0900Z 11.8N 31.7W 35 KT 40 MPH
12H 30/1800Z 12.5N 33.7W 40 KT 45 MPH
24H 31/0600Z 13.5N 36.8W 50 KT 60 MPH
36H 31/1800Z 14.4N 40.2W 60 KT 70 MPH
48H 01/0600Z 15.3N 43.7W 70 KT 80 MPH
72H 02/0600Z 17.0N 49.5W 80 KT 90 MPH
96H 03/0600Z 18.5N 54.0W 90 KT 105 MPH
120H 04/0600Z 20.5N 58.0W 100 KT 115 MPH

$$
FORECASTER BRENNAN

[abajan]

oh yeah the NOGAPS....that is my favorite....developes a nice TS over FL and moves it all the way to Texas.....


here is the full run

https://www.fnmoc.navy.mil/wxmap_cgi/cg ... t=Tropical

[phwxenthusiast]

it's a government website, what could possibly be wrong?? i have it bookmarked for almost a year now, no problems..

[Dydion]

Can someone direct me somewhere to where I can glean an understanding of headings and degrees...like 290, 270, etc., etc., that Larrywx extrapolated on in his earlier post on the headings and hits to the CONUS?

Thanks,

[Florida1118]

Welcome Katia. Now has M or Major at the end of her track.



Uploaded Image

[Gustywind]

Tropical Storm Katia forms

Dr. Rick Knabb, and Kevin Roth, The Weather Channel

Aug 30, 2011 4:53 am ET


- The depression over the far eastern Atlantic Ocean has been upgraded to Tropical Storm Katia.

- Katia is forecast to become a hurricane this week, but too soon to determine if any land areas will eventually be affected.

- Computer models are in excellent agreement that Katia should move north of the Leeward Islands over the weekend.

- However, that is a long way off and the forecast could change, so interests in the Leeward Islands should check back for future updates on Katia.

ATLANTIC BASIN

- Tropical Depression 12 was upgraded to Tropical Storm Katia this morning well southwest of the Cape Verde Islands.

- No threat to land for the next several days.

- Very likely to become a hurricane later this week, possibly Wednesday night or Thursday.

- Could reach the longitude of the Leeward Islands this weekend; while most models forecast the cyclone to pass north of the Leeward Islands, direct impacts there cannot yet be ruled out.

- While tropical depressions that initially form this far east have a greater chance of curving back out to sea before reaching the U.S., that is not yet certain to occur in this case.

- Too soon to determine what other land areas might eventually be affected.

[KWT]

I'm feeling a little more confident that Katia will end up recurving on a track not too different to Bill, so still a possible threat to E.Canada a long way down the line IMO...

[supercane]

Welcome to Storm2K, meriland23 and Dydion.

Dydion, here is a picture to help you out on compass headings:

[cycloneye]

This morning's discussion of Katia by Rob of Crown Weather:

The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

http://www.crownweather.com/?page_id=4557

Tropical Storm Katia:
Tropical Depression #12 has been upgraded to Tropical Storm Katia early this morning as the entire system is better organized. Currently there is 15 to 20 knots of shear affecting Katia and this shear is forecast to decrease by later today and tonight with intensification likely from this afternoon into this weekend. It is anticipated that Katia will reach hurricane strength during the day Wednesday and major hurricane strength by late this weekend.

Katia is tracking west-northwest at a forward speed of 16 to 17 mph and the storm is being steered by a ridge of high pressure located to the north. Yesterday, all of the global model guidance pointed to a likely scenario of Katia being steered out to sea due to a upper level low pressure system located over the central Atlantic. Since then the global models are trending towards a weaker and less amplified upper level low pressure system that lifts out with a ridge of high pressure rebuilding to the north of the storm. The latest GFS model forecasts a track that takes Katia to the north of the Leeward Islands and severely impacts Bermuda next Thursday. The European operational model forecasts a track that takes Katia to the north of the Lesser Antilles and then on a track northward halfway between the US East Coast and Bermuda. The ensemble members of the European model are further west than the operational model and imply a very close brush with the US East Coast with a 10 day forecast position of 28 North Latitude, 73.5 West Longitude. Two things to point out are that any further shifts to the south in the forecast track will put the northern Leeward Islands, the Virgin Islands and Puerto Rico at a significant threat from Katia. All of our friends in the northeastern Caribbean should closely monitor Katia. The second is that given the trends in the upper air pattern forecast, I suspect we may see further shifts to the west in the forecast track of Katia by the model guidance. It is way, way too early to be confident or certain on any one forecast track for Katia.

As of this morning, I am still leaning towards a track that takes Katia very close to, if not right over the northeastern Caribbean on Sunday and Monday followed by a track that takes Katia just east of the Bahamas next Wednesday and then northward near the US East Coast late next week and next weekend. The highest threat areas after moving away from the northeastern Caribbean for Katia are Bermuda, the Canadian Maritimes and possibly eastern New England.

[thetruesms]

For anyone who's curious, Chrome doesn't like the security certificate because the military self-signs them. Obviously a security risk for an entity to say "Trust me, you can because I say you can!", so that's why Chrome blocks it. If you feel you can take the Navy at their word that they won't do mean things to your computer, it's fine to go ahead. You can even download the certificate to your computer and import it into your certificate library so your browser won't complain anymore.

[Blown Away]

Obviously it's still very early, but the globals have been agreeing on a recurve NE of the Caribbean, maybe affecting Bermuda. Still no reason to think that persistent hole in the ridge won't be there when Katia hits @65W.

[KWT]

Indeed BA, there is good confidence with regards to that, however we've seen good confidence before at 168hrs be blown away by the time we get to 120hrs so who knows!

One thing I will say about Katia, the NHC are getting steadily more agressive with thier intensity forecasts now.

[HurricaneWarning92]

arent they forecasting a ridge building in to the north and west in the long term? How does that indicate there would be a definite gap for her to recurve?

[KWT]

There will be a ridge to the north of Katia in the short to medium term but its once this system gets to about 60-70W that there is well defined weakness which is present.

Thats a little too far out to be 100% confident, but its a feature that has been present pretty much constantly in the last 2 seasons.

[Dydion]

Thanks, supercane!