Tropical Storm Erika

[wxtrackercody]

Almost looks like two distinct competing circulations

 

Yup, I was just about to post this shortwave animation.

 

 

Observations from recon and from St. Croix support the northern one to be the more dominant feature.

[IsentropicLift]

Yup, I was just about to post this shortwave animation.

 

 

Observations from recon and from St. Croix support the northern one to be the more dominant feature.

FWIW the 00z NAM shows that as the emerging center with the convection continuing to be displaced to the East of the center.

 

[bobbutts]

The radar seems to show a tightening circulation just south of the radar site.  Is it really tightening or is that just due to the beam hitting lower in the clouds as it approaches?

[SN_Lover]

Looks like they found a 1011mb reading SE of the old location.

[wxmeddler]

The LLC near PR is really movin'... I got 266° at 33kts

[SN_Lover]

The LLC near PR is really movin'... I got 266° at 33kts

wounder why recon is not flying over there. im puzzled. 

[1234snow]

[wxtrackercody]

Recon is finding a pronounced shift at 15.3N. If that's the dominant center, Erika is all but dead. A relocation that far south would mean a track over a good chunk of Hispaniola.

 

I wish they would investigate the circulation near Puerto Rico.

[Coach McGuirk]

This thing is a mess.

[IsentropicLift]

Look at that new banding feature closer to the main convection. Now i know why models are bringing the center over PR because the one currently closer to the coast is racing off to the West and will miss.

 

http://radar.weather.gov/radar.php?product=NCR&rid=JUA&loop=yes

[turtlehurricane]

The circulation on puerto rico radar is definitely the dominate center. Satellite shows the center decoupling from convection.

 

If there is a circulation south of the dominant center it is simply a mid-level vorticity max associated with convection. Considering the vigorous nature of the circulation I don't expect a center relocation, but it will continue to be dragged south of track due to asymmetric convection, same behavior as the last couple days.

[turtlehurricane]

The next 12 hours will be absolutely crucial. If Erika goes too far south its current center will be mauled. It needs to be far enough north for the center to at least go along the northern coastline, if not put some distance between itself and the coast.

 

There will be vigorous orographic convection along the southern coast of hispaniola during the time of interaction. If the main center goes over the mountains then a new center would probably form along the southern coast of hispaniola, completely changing the track.

[SN_Lover]

The circulation on puerto rico radar is definitely the dominate center. Satellite shows the center decoupling from convection.

 

If there is a circulation south of the dominant center it is simply a mid-level vorticity max associated with convection. Considering the vigorous nature of the circulation I don't expect a center relocation, but it will continue to be dragged south of track due to asymmetric convection, same behavior as the last couple days.

Tell the hurricane hunters that. They seem to be on a planet of their own. 

[turtlehurricane]

The HWRF looks like the most realistic scenario to me based on current observations http://moe.met.fsu.edu/cgi-bin/hwrftc2.cgi?time=2015082718-erika05l&field=Sea+Level+Pressure&hour=Animation

[SN_Lover]

The HWRF looks like the most realistic scenario to me based on current observations http://moe.met.fsu.edu/cgi-bin/hwrftc2.cgi?time=2015082718-erika05l&field=Sea+Level+Pressure&hour=Animation

NAM came in with the same conclusion fwiw. 

[yoda]

Erika still a TS at 11pm adv

 

W at 17 mph

Winds 45 mph

16.6 N 65.3 W 

1008mb

[yoda]

[turtlehurricane]

They put the center in the completely wrong position, why would they do that? To preserve the old forecast?

 

That's gonna screw up all the model runs for sure, to initialize the vortex in the wrong spot.

[yoda]

 

TROPICAL STORM ERIKA DISCUSSION NUMBER 13
NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015
1100 PM AST THU AUG 27 2015

The center of Erika is not easy to locate tonight, and it
appears that a few smaller swirls are rotating within a larger
gyre. In fact, one of these small swirls moved near St. Croix
producing tropical storm force wind gusts during the past few
hours on the island. Due to the lack of an inner core, the initial
position is based on a mean center of circulation. Despite the poor
organization, the reconnaissance plane currently in Erika was able
to measure 700 mb flight-level winds of 59 kt well to the southeast
of the alleged center. Based on the SFMR, these winds are not at the
surface, and the initial intensity is kept at 40 kt. The central
pressure is not falling, which is another indication that Erika is
not strengthening. The NHC forecast calls for no change in intensity
during the next 36 hours, given the fact that cyclone will be
moving through a very hostile shear environment, and will also feel
the effects of land. Once in the Bahamas, however, the upper-level
flow is expected to become more favorable, and if Erika survives, it
has the opportunity to strengthen some. The NHC forecast is very
close to the intensity consensus and is similar to the previous one.

The best estimate of the initial motion is toward the west or 270
degrees at 15 kt, and this estimate is highly uncertain. Erika
should begin to turn toward the west-northwest during the next
several hours around the periphery of the western Atlantic
subtropical ridge, and should reach the Central Bahamas between 36
and 48 hours. By then, the cyclone will be located on the
southwestern edge of the ridge, and should begin to turn to the
northwest with decreasing forward speed. Most of the track
guidance, including the ECMWF and the GFS global models, show a
tropical cyclone approaching southeast Florida in about 3 days and
moving northward near or over the east coast of Florida during the
latter portion of the forecast period. There is unusually high
uncertainty in this forecast, especially at days 3 to 5, given that
the cyclone has to recover from shear and from the effects of
land for this to occur.

The greatest short-term threat posed by Erika continues to be
very heavy rainfall over portions of the northern Leeward Islands
tonight, and over the Virgin Islands and Puerto Rico on Friday.
These rains could produce flash floods and mud slides.


FORECAST POSITIONS AND MAX WINDS

INIT 28/0300Z 16.6N 65.3W 40 KT 45 MPH
12H 28/1200Z 18.2N 67.4W 40 KT 45 MPH
24H 29/0000Z 19.7N 70.2W 40 KT 45 MPH
36H 29/1200Z 21.1N 73.2W 40 KT 45 MPH
48H 30/0000Z 22.5N 75.5W 45 KT 50 MPH
72H 31/0000Z 25.2N 79.0W 55 KT 65 MPH
96H 01/0000Z 27.3N 80.2W 65 KT 75 MPH
120H 02/0000Z 29.5N 80.7W 75 KT 85 MPH

$

Forecaster Avila

[IsentropicLift]

ZCZC MIATCDAT5 ALL
TTAA00 KNHC DDHHMM

TROPICAL STORM ERIKA DISCUSSION NUMBER 13
NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015
1100 PM AST THU AUG 27 2015

The center of Erika is not easy to locate tonight, and it
appears that a few smaller swirls are rotating within a larger
gyre. In fact, one of these small swirls moved near St. Croix
producing tropical storm force wind gusts during the past few
hours on the island. Due to the lack of an inner core, the initial
position is based on a mean center of circulation. Despite the poor
organization, the reconnaissance plane currently in Erika was able
to measure 700 mb flight-level winds of 59 kt well to the southeast
of the alleged center. Based on the SFMR, these winds are not at the
surface, and the initial intensity is kept at 40 kt. The central
pressure is not falling, which is another indication that Erika is
not strengthening. The NHC forecast calls for no change in intensity
during the next 36 hours, given the fact that cyclone will be
moving through a very hostile shear environment, and will also feel
the effects of land. Once in the Bahamas, however, the upper-level
flow is expected to become more favorable, and if Erika survives, it
has the opportunity to strengthen some. The NHC forecast is very
close to the intensity consensus and is similar to the previous one.

The best estimate of the initial motion is toward the west or 270
degrees at 15 kt, and this estimate is highly uncertain. Erika
should begin to turn toward the west-northwest during the next
several hours around the periphery of the western Atlantic
subtropical ridge, and should reach the Central Bahamas between 36
and 48 hours. By then, the cyclone will be located on the
southwestern edge of the ridge, and should begin to turn to the
northwest with decreasing forward speed. Most of the track
guidance, including the ECMWF and the GFS global models, show a
tropical cyclone approaching southeast Florida in about 3 days and
moving northward near or over the east coast of Florida during the
latter portion of the forecast period. There is unusually high
uncertainty in this forecast, especially at days 3 to 5, given that
the cyclone has to recover from shear and from the effects of
land for this to occur.

The greatest short-term threat posed by Erika continues to be
very heavy rainfall over portions of the northern Leeward Islands
tonight, and over the Virgin Islands and Puerto Rico on Friday.
These rains could produce flash floods and mud slides.


FORECAST POSITIONS AND MAX WINDS

INIT 28/0300Z 16.6N 65.3W 40 KT 45 MPH
12H 28/1200Z 18.2N 67.4W 40 KT 45 MPH
24H 29/0000Z 19.7N 70.2W 40 KT 45 MPH
36H 29/1200Z 21.1N 73.2W 40 KT 45 MPH
48H 30/0000Z 22.5N 75.5W 45 KT 50 MPH
72H 31/0000Z 25.2N 79.0W 55 KT 65 MPH
96H 01/0000Z 27.3N 80.2W 65 KT 75 MPH
120H 02/0000Z 29.5N 80.7W 75 KT 85 MPH

$

[turtlehurricane]

Well they totally screwed that analysis and forecast up, that's for damn sure. Doesn't make a huge difference but surprising in a bad way.

 

I do not see several swirls, there is 1 clearly defined center on radar and satellite. If they're getting confused by mid-level vortices in convection that's kind've sad.

[IsentropicLift]

[turtlehurricane]

If the shear vector switches from northerly to southerly like that map shows, that could be the wild card. Imagine if the center re-formed in convection off the north coast of Hispaniola...

[wxtrackercody]

¯\_(ツ)_/¯

 

[Typhoon Tip]

Well they did say they were taking the mean of all the possible centers that they did detect also confirming earlier suspicions as we talked about it - there were more than one. The mean may not represent the previous fix trajectory so that much could easily be explained. It's poorly organized in the most obvious center just happens to be the one that's detectable by radar but they could be more than one out there still in fact that convective blob more to the South seems to be taking on-site want to curl of its own. Wouldnt itbe fascinating of the sink split into two distinct systems

[IsentropicLift]

The GFS initilaized with the Southern circulation as the center, close to where the NHC placed it, not sure what role the NHC placement had if any on the current run, but earlier remarks stated that the new data would in the 00z GFS.

[ncforecaster89]

Well they totally screwed that analysis and forecast up, that's for damn sure. Doesn't make a huge difference but surprising in a bad way.

I do not see several swirls, there is 1 clearly defined center on radar and satellite. If they're getting confused by mid-level vortices in convection that's kind've sad.

I whole-heartedly concur with the main premise of this post! The choice to select a "mean" center for the initial position estimate isn't one I agree with, either, and suspect it was chosen to maintain more forecast continuity - in the absence of much confidence in the true position of the main COC.

As has been pointed out by others previously...I too don't understand why RECON wasn't directed to investigate the more evident circulation (visble on both satellite and radar) just to the SE of PR.

EDIT: The main point being that I feel it was prudent to have at least investigated the aforementioned prospective COC to make a more accurate assessment of Erika's structure. As most of us know, it will not be surprising to see multiple relocations of the dominate COC until Erika becomes much better organized, if it ever does so.

[Disc]

The LLC is really cruising. 

 

[IsentropicLift]

In any event the GFS rams the center right into Hispaniola and the system seems to regenerate North of Haiti in about 24 hours.

[BuffaloWeather]

The LLC is really cruising. 

 

 

That's quite an understatement. lol