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Hurricane Katia


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Arguments about track should have ended several days ago.

someone forgot to inform the british

THE UKMET MODEL HAS BEEN STUBBORNLY FORECASTINGA MUCH STRONGER RIDGE...WHICH FORCES THE CYCLONE ON A WESTWARDCOURSE CLOSER TO THE BAHAMAS. THIS WESTWARD TRACK SEEMS HIGHLYUNLIKELY DUE TO A PRONOUNCED TROUGH OVER THE WESTERN ATLANTIC OCEANAND THE UKMET SOLUTION IS DISREGARDED FOR THIS FORECAST.

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No meaningful changes in my thoughts this morning...

1. Recurvature remains the most likely outcome.

2. Model agreement toward recurvature has increased as the westward trend in the modeling ended yesterday. The models have grown less impressed with the ridging that will try to redevelop and steer Katia back to the west for the time. Hence, following a short period of a more westerly component to Katia's track, the models make a quicker turn toward recurvature away from the U.S.

3. The 9/3 0z UKMET is already off by 90 miles from Katia's position (Katia is well to the east of the UKMET's forecast). That model, along with the Nogaps, is not likely to verify given the magnitude of its early error.

4. The most likely tropical impact in the Mid-Atlantic and Northeast will come from the remnants of Lee merging with an approaching cold front. That could bring a significnt rainfall to portions of the Mid-Atlantic region and possibly into southern New England next week.

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The biggest key here is the upper low in the OH Valley that is forecast to develop at about day 6-7. The farther west and deeper this is, the better chance Katia can slingshot around it and into New England- which is what the new CMC has. Still not convinced that this will actually happen, lots of variables including Lee, the strength of Katia etc etc. An extremely complex scenario.

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someone forgot to inform the british

THE UKMET MODEL HAS BEEN STUBBORNLY FORECASTINGA MUCH STRONGER RIDGE...WHICH FORCES THE CYCLONE ON A WESTWARDCOURSE CLOSER TO THE BAHAMAS. THIS WESTWARD TRACK SEEMS HIGHLYUNLIKELY DUE TO A PRONOUNCED TROUGH OVER THE WESTERN ATLANTIC OCEANAND THE UKMET SOLUTION IS DISREGARDED FOR THIS FORECAST.

The 12z UKMET finally awakened from its dreams. It now recognizes the turn northward.

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The biggest key here is the upper low in the OH Valley that is forecast to develop at about day 6-7. The farther west and deeper this is, the better chance Katia can slingshot around it and into New England- which is what the new CMC has. Still not convinced that this will actually happen, lots of variables including Lee, the strength of Katia etc etc. An extremely complex scenario.

It's interesting to watch the model gymnastics which are probably a day or two away from settling. The Euro rolls in now further west, after 72/75 hours it's rolling due west or wnw. By 102 hours it's getting much more interesting as well.

The 12z Euro is hundres of miles SW of the 0z run.

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Euro turns it a hundred or two miles east of Hatteras, then skims by east of Cape Cod. A real close but no cigar run.

True but at H162 12z vs h1740z it has moved about 500 miles WSW in a single run.GFS v Euro spread at that same time is 750 miles...quite a lot of uncertainty.

ADMIN NOTE: Tons of posts aren't appearing/failing. I know I'm not alone, it appears the DB just loses them and instead of ending up back on the forum thread you get dumped to the homepage.

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True but at H162 12z vs h1740z it has moved about 500 miles WSW in a single run.GFS v Euro spread at that same time is 750 miles...quite a lot of uncertainty.

It is an impressive turn of events. The Euro is a shade to the west of what remains one of my top two analogs for Katia (Hurricane #1 in 1927; Gladys in 1975 is my other one, but the former is probably ahead of it at this time). My full set of 10 analogs (Message #561 in this thread) remains the same from yesterday.

http://weather.unisy...927/1/track.gif

My guess about Katia's track remains unchanged for now:

17.5N 52.8W; Actual: 17.5N 52.4; Error: 26 miles--1.5 hours in advance

20.0N 56.8W

25.0N 63.9W

30.0N 72.0W

35.0N 69.6W

40.0N 63.5W

Given the recent GGEM and ECMWF runs, I suspect that the positions for 35N and 40N will need to be adjusted to the west. While I still favor recurvature (IMO, about a 67% probability), I still do not believe U.S. landfall can or should be ruled out.

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It is an impressive turn of events. The Euro is a shade to the west of what remains one of my top two analogs for Katia (Hurricane #1 in 1927; Gladys in 1975 is my other one, but the former is probably ahead of it at this time). My full set of 10 analogs (Message #561 in this thread) remains the same from yesterday.

http://weather.unisy...927/1/track.gif

My guess about Katia's track remains unchanged for now:

17.5N 52.8W; Actual: 17.5N 52.4; Error: 26 miles--1.5 hours in advance

20.0N 56.8W

25.0N 63.9W

30.0N 72.0W

35.0N 69.6W

40.0N 63.5W

Given the recent GGEM and ECMWF runs, I suspect that the positions for 35N and 40N will need to be adjusted to the west. While I still favor recurvature (IMO, about a 67% probability), I still do not believe U.S. landfall can or should be ruled out.

Good analysis, I agree with your conclusions.

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It is an impressive turn of events. The Euro is a shade to the west of what remains one of my top two analogs for Katia (Hurricane #1 in 1927; Gladys in 1975 is my other one, but the former is probably ahead of it at this time). My full set of 10 analogs (Message #561 in this thread) remains the same from yesterday.

http://weather.unisy...927/1/track.gif

My guess about Katia's track remains unchanged for now:

17.5N 52.8W; Actual: 17.5N 52.4; Error: 26 miles--1.5 hours in advance

20.0N 56.8W

25.0N 63.9W

30.0N 72.0W

35.0N 69.6W

40.0N 63.5W

Given the recent GGEM and ECMWF runs, I suspect that the positions for 35N and 40N will need to be adjusted to the west. While I still favor recurvature (IMO, about a 67% probability), I still do not believe U.S. landfall can or should be ruled out.

Great write up Don. Family and I got into Orlando this morning, and I must say, I can't be happier with sitting between these two vacation busters! (Lee and Katia). However, the return home next Friday (flying) just became a tad more interesting. Models having all sorts of issues with Lee....if he weren't around, I thing the model spread word certainly be narrower. Still over a 50% recurve, but each day seems to shave a few percent off that scenario.

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It is an impressive turn of events. The Euro is a shade to the west of what remains one of my top two analogs for Katia (Hurricane #1 in 1927; Gladys in 1975 is my other one, but the former is probably ahead of it at this time). My full set of 10 analogs (Message #561 in this thread) remains the same from yesterday.

http://weather.unisy...927/1/track.gif

My guess about Katia's track remains unchanged for now:

17.5N 52.8W; Actual: 17.5N 52.4; Error: 26 miles--1.5 hours in advance

20.0N 56.8W

25.0N 63.9W

30.0N 72.0W

35.0N 69.6W

40.0N 63.5W

Given the recent GGEM and ECMWF runs, I suspect that the positions for 35N and 40N will need to be adjusted to the west. While I still favor recurvature (IMO, about a 67% probability), I still do not believe U.S. landfall can or should be ruled out.

Yeah, I agree Don :thumbsup: GGEM definately has done well with this storm. It has one of the lowest average position errors. I think a blend of the GGEM and ECMWF will do pretty well for this forecast period.

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...KATIA SPARRING WITH STRONG UPPER-LEVEL WINDS...KNOCKED DOWN TO A TROPICAL STORM FOR THE SECOND TIME...

5:00 PM AST Sat Sep 3

Location: 19.9°N 56.8°W

Max sustained: 70 mph

Moving: WNW at 10 mph

Min pressure: 993 mb

IT CANNOT BE STRESSED ENOUGH THAT THERE IS CONSIDERABLE UNCERTAINTY

IN THE TRACK FORECAST...WHICH IS EXTREMELY SENSITIVE TO THE

EVOLUTION OF TROPICAL STORM LEE AND ITS INTERACTION WITH A MID-

TO UPPER-LEVEL LOW OVER THE EASTERN UNITED STATES. THE MODEL

GUIDANCE IS IN PRETTY GOOD AGREEMENT DURING THE FIRST 36 HOURS OR

SO...BUT THE DIVERGENCE ONLY GROWS FROM THERE. COMPARED TO THE

PREVIOUS FORECAST CYCLE...THE UKMET HAS SHIFTED TO THE NORTH AND

THE GFS HAS SLOWED DOWN...WHICH NORMALLY WOULD HAVE INCREASED

CONFIDENCE IN THE FORECAST. FURTHERMORE...THE ECMWF...WHICH IS

NORMALLY RELIABLE...SWUNG FROM THE NORTH AND EAST SIDE OF THE

GUIDANCE TO THE SOUTH AND WEST SIDE...SHOWING A MORE WESTWARD

MOTION BY DAY 5. THE OFFICIAL TRACK FORECAST HAS BEEN NUDGED A BIT

TO THE WEST TOWARDS THE VARIOUS CONSENSUS MODELS...BUT WE WOULD

RATHER SEE SOME STABILITY IN THE MODELS BEFORE MAKING A LARGER

SHIFT.

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DISCUSSION AND 48-HOUR OUTLOOK

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

AT 500 PM AST...2100 UTC...THE CENTER OF TROPICAL STORM KATIA WAS

LOCATED NEAR LATITUDE 19.9 NORTH...LONGITUDE 56.8 WEST. KATIA IS

MOVING TOWARD THE WEST-NORTHWEST NEAR 10 MPH...17 KM/H...AND THIS

GENERAL MOTION IS EXPECTED TO CONTINUE THROUGH MONDAY.

MAXIMUM SUSTAINED WINDS HAVE DECREASED TO NEAR 70 MPH...110

KM/H...WITH HIGHER GUSTS. FLUCTUATIONS IN INTENSITY ARE POSSIBLE

OVER THE NEXT DAY OR SO...AND KATIA COULD RE-STRENGTHEN BACK TO A

HURRICANE AT ANY TIME.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 140 MILES...220 KM

FROM THE CENTER.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 993 MB...29.32 INCHES.

I'm suprised to see such a straight tropical storm wind prob cone rather than a curved one

205114.gif

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