ATL : TROPICAL DEPRESSION ERIKA (06L)

[Aric Dunn]

the longer it waits to get moving wouldnt give it more of a chance to take a westerly path?

actually yes.. hence the models reacted to the lack of forward motion and shifted slightly west. the longer it hangs back the more west it could make it according to the lasted models synoptics..

How so if it deepens, for example should hook more northward even quicker wouldn't you think given an approaching trough rolling off the Eastern CONUS in 84 hours (NAM depicts this trough well)? What makes you think more west if it stalls?

even if it deepens the ridge is supposed to build west with the system .. which should still keep it on a more westerly track if it is slower than originally forecast.

['CaneFreak]

..

What was that Aric? You are drunk? I didn't catch that...???

[Dean4Storms]

Still appears to be sheared with the mid-upper circulation to the east of the LLC. Add in some dry air and it may only slowly strengthen till it gets stacked and then lookout!

[boca]

If theirs a trough approaching the east coast in 84hrs wouldn't that force a northerly turn?

[Aric Dunn]

Still appears to be sheared with the mid-upper circulation to the east of the LLC. Add in some dry air and it may only slowly strengthen till it gets stacked and then lookout!

the funny thing is.. the both the mid level and upper level shear is in a different direction the where the convection is displaced.. so i cant buy that yet.. the dry air is probably the most likely casue..

when recon get back out there we will know if the center has relocated.

[Evil Jeremy]

If theirs a trough approaching the east coast in 84hrs wouldn't that force a northerly turn?

The strength of the ridge, the strength of the trough, the strength of the storm, to many factors in the equation lol. Nothing is definite. This is a complex setup.

[boca]

If theirs a trough approaching the east coast in 84hrs wouldn't that force a northerly turn?

The strength of the ridge, the strength of the trough, the strength of the storm, to many factors in the equation lol. Nothing is definite. This is a complex setup.

It is too complex especially if it stalls.

[Aric Dunn]

If theirs a trough approaching the east coast in 84hrs wouldn't that force a northerly turn?

well yeah if it was close enough ..
the ridge is supposed to build west ahead of the trough farther south .. which will keep her more west and south .. then as it comes to the south west side of the ridge is when things get tricky as the the timing is key. if its slow the trough will pull out, and all models no matter if it re-curves or not build this ridge south . so the timing of when it approaches the sw side of the ridge is very important..

[Brent]

TROPICAL STORM ERIKA FORECAST/ADVISORY NUMBER 2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062009
0300 UTC WED SEP 02 2009

A TROPICAL STORM WATCH REMAINS IN EFFECT FOR ST.
MAARTEN...ANTIGUA...BARBUDA...ST. KITTS...NEVIS...ANGUILLA...ST.
MARTIN AND ST. BARTHELEMY.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 36 HOURS.

INTERESTS ELSEWHERE IN THE NORTHERN LEEWARD ISLANDS...U.S. AND
BRITISH VIRGIN ISLANDS...AND PUERTO RICO SHOULD MONITOR THE
PROGRESS OF ERIKA.

TROPICAL STORM CENTER LOCATED NEAR 17.5N 57.6W AT 02/0300Z
POSITION ACCURATE WITHIN 30 NM

PRESENT MOVEMENT TOWARD THE WEST-NORTHWEST OR 300 DEGREES AT 7 KT

ESTIMATED MINIMUM CENTRAL PRESSURE 1004 MB
MAX SUSTAINED WINDS 50 KT WITH GUSTS TO 60 KT.
50 KT....... 30NE 0SE 0SW 0NW.
34 KT.......105NE 90SE 0SW 50NW.
12 FT SEAS..150NE 90SE 0SW 50NW.
WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL
MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT.

REPEAT...CENTER LOCATED NEAR 17.5N 57.6W AT 02/0300Z
AT 02/0000Z CENTER WAS LOCATED NEAR 17.3N 57.3W

FORECAST VALID 02/1200Z 18.0N 58.7W
MAX WIND 55 KT...GUSTS 65 KT.
50 KT... 30NE 0SE 0SW 0NW.
34 KT...105NE 90SE 0SW 0NW.

FORECAST VALID 03/0000Z 18.5N 60.2W
MAX WIND 60 KT...GUSTS 75 KT.
50 KT... 45NE 0SE 0SW 0NW.
34 KT...120NE 90SE 30SW 45NW.

FORECAST VALID 03/1200Z 19.0N 61.8W
MAX WIND 60 KT...GUSTS 75 KT.
50 KT... 45NE 0SE 0SW 0NW.
34 KT...120NE 90SE 45SW 60NW.

FORECAST VALID 04/0000Z 19.5N 63.2W
MAX WIND 55 KT...GUSTS 65 KT.
50 KT... 45NE 30SE 0SW 30NW.
34 KT...120NE 90SE 45SW 60NW.

FORECAST VALID 05/0000Z 21.0N 66.0W
MAX WIND 50 KT...GUSTS 60 KT.
50 KT... 45NE 30SE 0SW 30NW.
34 KT...120NE 90SE 45SW 60NW.

EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 225 NM
ON DAY 4 AND 300 NM ON DAY 5...AND FOR INTENSITY NEAR 20 KT EACH DAY

OUTLOOK VALID 06/0000Z 22.6N 68.4W
MAX WIND 45 KT...GUSTS 55 KT.

OUTLOOK VALID 07/0000Z 24.5N 71.0W
MAX WIND 45 KT...GUSTS 55 KT.

REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 17.5N 57.6W

NEXT ADVISORY AT 02/0900Z

$$
FORECASTER AVILA

BULLETIN
TROPICAL STORM ERIKA ADVISORY NUMBER 2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062009
1100 PM AST TUE SEP 01 2009

...ERIKA MOVING VERY SLOWLY...

A TROPICAL STORM WATCH REMAINS IN EFFECT FOR ST. MAARTEN...
ANTIGUA...BARBUDA...ST. KITTS...NEVIS...ANGUILLA...ST.
MARTIN AND ST. BARTHELEMY.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 36 HOURS.

INTERESTS ELSEWHERE IN THE NORTHERN LEEWARD ISLANDS...U.S. AND
BRITISH VIRGIN ISLANDS...AND PUERTO RICO SHOULD MONITOR THE
PROGRESS OF ERIKA.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED
STATES...INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE
MONITOR PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE
FORECAST OFFICE. FOR STORM INFORMATION SPECIFIC TO YOUR AREA
OUTSIDE OF THE UNITED STATES...PLEASE MONITOR PRODUCTS ISSUED
BY YOUR NATIONAL METEOROLOGICAL SERVICE.

AT 1100 PM AST...0300 UTC...THE CENTER OF TROPICAL STORM ERIKA WAS
LOCATED NEAR LATITUDE 17.5 NORTH...LONGITUDE 57.6 WEST OR ABOUT 365
MILES...585 KM...EAST OF THE NORTHERN LEEWARD ISLANDS.

ERIKA HAS BEEN MEANDERING FOR THE PAST FEW HOURS...BUT IT SHOULD
BEGIN TO MOVE TOWARD THE WEST-NORTHWEST NEAR 8 MPH...13 KM/HR ON
WEDNESDAY. ON THIS TRACK...THE CENTER OF ERIKA IS EXPECTED TO
PASS TO THE NORTHEAST OF THE LEEWARD ISLANDS ON THURSDAY.

MAXIMUM SUSTAINED WINDS HAVE INCREASED TO NEAR 60 MPH...95
KM/HR...WITH HIGHER GUSTS. SOME STRENGTHENING IS POSSIBLE DURING
THE NEXT 24 HOURS.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 120 MILES...195 KM
MAINLY TO THE NORTH AND EAST OF THE CENTER.

THE MINIMUM CENTRAL PRESSURE REPORTED BY AN AIR FORCE RECONNAISSANCE
AIRCRAFT WAS 1004 MB...29.65 INCHES.

ERIKA IS EXPECTED TO PRODUCE TOTAL RAINFALL ACCUMULATIONS OF 2 TO 4
INCHES OVER THE NORTHERN LEEWARD ISLANDS DURING THE NEXT COUPLE OF
DAYS...WITH POSSIBLE ISOLATED MAXIMUM AMOUNTS OF 6 INCHES.

...SUMMARY OF 1100 PM AST INFORMATION...
LOCATION...17.5N 57.6W
MAXIMUM SUSTAINED WINDS...60 MPH
PRESENT MOVEMENT...WEST-NORTHWEST OR 300 DEGREES AT 8 MPH
MINIMUM CENTRAL PRESSURE...1004 MB

AN INTERMEDIATE ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE
CENTER AT 200 AM AST FOLLOWED BY THE NEXT COMPLETE ADVISORY AT 500
AM AST.

$$
FORECASTER AVILA

TROPICAL STORM ERIKA DISCUSSION NUMBER 2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062009
1100 PM AST TUE SEP 01 2009

AN AIR FORCE RECONNAISSANCE PLANE HAS BEEN TRAVERSING ERIKA AND
FOUND THAT THE CENTER HAS MOVED VERY LITTLE DURING THE PAST SEVERAL
HOURS. THE CIRCULATION HAS BECOME BETTER ESTABLISHED AND THE
MINIMUM CENTRAL PRESSURE FROM A DROP WAS 1004 MB. THIS VALUE COULD
BE A LITTLE BIT LOWER SINCE THE DROP MEASURED 19 KNOTS AT THE
SURFACE. THE SFMR AND THE PLANE MEASURED 55 AND 50 KNOTS...
RESPECTIVELY...TO THE NORTHEAST OF THE CENTER. THEREFORE...THE
INITIAL INTENSITY IS SET AT 50 KNOTS. THERE HAS BEEN AN INCREASE IN
CONVECTION NEAR THE CENTER AND THERE ARE SOME INDICATIONS FROM THE
HIGH-CLOUD MOTION THAT THE SHEAR HAS LESSENED A LITTLE BIT. ERIKA
COULD STRENGTHEN SOME DURING THE NEXT DAY OR TWO. THEREAFTER...MOST
OF THE GLOBAL MODELS HAVE STRONG UPPER-LEVEL WESTERLY WINDS OVER
ERIKA...A PATTERN THAT IS NOT FAVORABLE FOR STRENGTHENING. IN
FACT...THE OFFICIAL FORECAST CALLS FOR WEAKENING DURING THAT PERIOD
AS OPPOSED TO THE GFDL AND HWRF THAT BOTH MAKE ERIKA A STRONG
HURRICANE.

ERIKA HAS BEEN MOVING VERY LITTLE DURING THE PAST FEW HOURS...BUT
THIS COULD BE THE RESULT OF THE CYCLONE BEING IN ITS FORMATIVE
STAGE. ERIKA IS LOCATED ON THE SOUTHWESTERN EDGE OF THE
AZORES-BERMUDA HIGH AND THE CYCLONE SHOULD BEGIN TO MOVE TOWARD THE
WEST-NORTHWEST OR 300 DEGREES AT 7 KNOTS ON WEDNESDAY. BECAUSE THE
AZORES-BERMUDA HIGH IS FORECAST TO EXPAND WESTWARD A LITTLE
BIT...ERIKA SHOULD MAINTAIN THIS WEST-NORTHWEST TO NORTHWEST TRACK.
SINCE THE STEERING CURRENTS ARE NOT VERY STRONG....ERIKA SHOULD
MOVE SLOWLY. GUIDANCE IS NOT IN GOOD AGREEMENT AND THE CONFIDENCE
IN THE FORECAST TRACK IS LOW. BOTH THE UK AND THE GFS TAKE A MORE
WESTWARD TRACK WHILE THE OTHER MODELS SHOW A MORE NORTHWESTERLY
COMPONENT. THE OFFICIAL FORECAST IS VERY CLOSE TO THE CONSENSUS
WHICH IS CENTERED BETWEEN THESE TWO MODEL OPTIONS.


FORECAST POSITIONS AND MAX WINDS

INITIAL 02/0300Z 17.5N 57.6W 50 KT
12HR VT 02/1200Z 18.0N 58.7W 55 KT
24HR VT 03/0000Z 18.5N 60.2W 60 KT
36HR VT 03/1200Z 19.0N 61.8W 60 KT
48HR VT 04/0000Z 19.5N 63.2W 55 KT
72HR VT 05/0000Z 21.0N 66.0W 50 KT
96HR VT 06/0000Z 22.6N 68.4W 45 KT
120HR VT 07/0000Z 24.5N 71.0W 45 KT

$$
FORECASTER AVILA

[wxman57]

New forecast is out. 24.5N/71W at 120 hrs - same as 21Z. 50 kts now.

[cycloneye]

[btangy]

The convection that is currently displaced downshear is probably being forced in part by jet dynamics and partly due to the strong low level flow running into the vortex and being forced to ascend on the E flank. What you're seeing is akin to a Midwest supercell in the deep tropics. I don't see this being sustained once Erika moves further W. There's a monster trough over the C Caribbean and it's not budging. Assuming it's in no hurry to move, Erika is going to run into this shear axis and bigger storms have dissipated as a result. Once Erika loses its upper level support, poof. As I see it right now, the shear has an ace showing and the odds are stacked against Erika's survival past 72 hours.

[Aric Dunn]

The discussion is good..

[CYCLONE MIKE]

If theirs a trough approaching the east coast in 84hrs wouldn't that force a northerly turn?

well yeah if it was close enough ..
the ridge is supposed to build west ahead of the trough farther south .. which will keep her more west and south .. then as it comes to the south west side of the ridge is when things get tricky as the the timing is key. if its slow the trough will pull out, and all models no matter if it re-curves or not build this ridge south . so the timing of when it approaches the sw side of the ridge is very important..

What are you seeing as to how strong this trough will be in 3-4 days. Some say weak and washing out, some say strong and deepening? Then the high is the other issue. Basically the same thing. Weak and others say fairly strong and expanding west/southwest.

[Evil Jeremy]

Still heading west 84 hours out on the NAM:

[Aric Dunn]

The convection that is currently displaced downshear is probably being forced in part by jet dynamics and partly due to the strong low level flow running into the vortex and being forced to ascend on the E flank. What you're seeing is akin to a Midwest supercell in the deep tropics. I don't see this being sustained once Erika moves further W. There's a monster trough over the C Caribbean and it's not budging. Assuming it's in no hurry to move, Erika is going to run into this shear axis and bigger storms have dissipated as a result. Once Erika loses its upper level support, poof. As I see it right now, the shear has an ace showing and the odds are stacked against Erika's survival past 72 hours.

I agree in the convection pattern, but not sure about the trough. it is very large but has been steadily weakening today and may not play such a weakening role of for the first 72 hours.

[artist]

The convection that is currently displaced downshear is probably being forced in part by jet dynamics and partly due to the strong low level flow running into the vortex and being forced to ascend on the E flank. What you're seeing is akin to a Midwest supercell in the deep tropics. I don't see this being sustained once Erika moves further W. There's a monster trough over the C Caribbean and it's not budging. Assuming it's in no hurry to move, Erika is going to run into this shear axis and bigger storms have dissipated as a result. Once Erika loses its upper level support, poof. As I see it right now, the shear has an ace showing and the odds are stacked against Erika's survival past 72 hours.

I really appreciate your posts, sharing your expertise with us. Thanks for taking the time to explain things.

Same goes to all others that take that time as well.

[AtlanticWind]

GUIDANCE IS NOT IN GOOD AGREEMENT AND THE CONFIDENCE
IN THE FORECAST TRACK IS LOW. BOTH THE UK AND THE GFS TAKE A MORE
WESTWARD TRACK WHILE THE OTHER MODELS SHOW A MORE NORTHWESTERLY
COMPONENT. THE OFFICIAL FORECAST IS VERY CLOSE TO THE CONSENSUS
WHICH IS CENTERED BETWEEN THESE TWO MODEL OPTIONS.

Still many questions on the future path.

[lonelymike]

The convection that is currently displaced downshear is probably being forced in part by jet dynamics and partly due to the strong low level flow running into the vortex and being forced to ascend on the E flank. What you're seeing is akin to a Midwest supercell in the deep tropics. I don't see this being sustained once Erika moves further W. There's a monster trough over the C Caribbean and it's not budging. Assuming it's in no hurry to move, Erika is going to run into this shear axis and bigger storms have dissipated as a result. Once Erika loses its upper level support, poof. As I see it right now, the shear has an ace showing and the odds are stacked against Erika's survival past 72 hours.

Interesting maybe the Good for $%^& is actually on to something.

[Aric Dunn]

If theirs a trough approaching the east coast in 84hrs wouldn't that force a northerly turn?

well yeah if it was close enough ..
the ridge is supposed to build west ahead of the trough farther south .. which will keep her more west and south .. then as it comes to the south west side of the ridge is when things get tricky as the the timing is key. if its slow the trough will pull out, and all models no matter if it re-curves or not build this ridge south . so the timing of when it approaches the sw side of the ridge is very important..

What are you seeing as to how strong this trough will be in 3-4 days. Some say weak and washing out, some say strong and deepening? Then the high is the other issue. Basically the same thing. Weak and others say fairly strong and expanding west/southwest.

the models all at some point either wash out the trough or lift it out and the timing is important. if she moves quicker than a re-curve is a likely path. if its slower than a more westward track and missing the trough all together is probable. its too early to say.

once she starts moving at least at a steady pace we will get a better model guidance