Friday Map Discussion: 31 August 2007

All attachments: http://www.atmos.albany.edu/student/heathera/mapdisc_08-31-07/

Hi Folks,

Friday map discussion resumed for the new 2007-08 academic year on 31Aug'07. Although tempted to do otherwise, we deferred discussion on the noteworthy temperature and rainfall anomalies of the summer of 2007 for a later Friday when all of the data is available. Instead, the focus was on the synoptic- and subsynoptic-scale features that controlled the life cycles of TS Erin and TC Dean. A brief postscript will be devoted to the likely unnamed TS of 30-31 Aug'07 off the Mid-Atlantic coast. Attached are images of the pressure on the dynamic tropopause (DT), the deep-layer (850 to DT) shear, and the925-850 hPa layer-averaged relative vorticity for selected time periods. These images were derived from Ron McTaggart-Cowan's GFS animation builder (link is provided below). Make your own loop to help fill in the gaps in the discussion and to construct alternative interpretations of events.

0000 UTC 10Aug:

Massive ridge overlies the central and eastern US. Deep easterly shear is present to the south of the ridge over the Gulf of Mexico. Cutoff low (PV anomaly) that will eventually interact with TS Erin is in the process of breaking away from a PV tail east of the Bahamas.

0000 UTC 13Aug:

Aforementioned PV anomaly moved westward across southern FL and is now located west of Key West, FL, where it is interacting with low-level vorticity that will eventually become TS Erin near the southern coast of western Cuba. Cyclonic deep-layer shear indicates that the PV anomaly is cold core (weak anticyclonic shear prevails over the low-level vorticity maximum, however).Increase in wind speeds to at buoy 44004

0000 UTC 16Aug:

TS Erin, embedded in anticyclonic deep-layer shear (850 hPa-DT), is approaching the south coast of TX. The PV anomaly that help to organize the initial low-level vorticity that became TS Erin has separately itself from Erin and is now over western TX.

Anew PV anomaly that will interact with TC Dean is in the process of forming northeast of the Bahamas along the southern end of a PV tail.

0000 UTC 19Aug:

The low-level vorticity maximum that nicely defines TS Erin (very much alive and kicking over OK and almost better defined than at landfall over TX) can be seen near 35 N and 100 W. it still has a warm-core structure based on the deep-layer anticyclonic shear indicated over the low-level vorticity maximum. The PV anomaly that originally helped to spark the development of the low-level vorticity maximum that became Erin is situated near39-40 N and 97-98 W and is defined by higher pressure on the DT. This DT feature, weakly cold core, helped to pump tropical moisture from Erin into a midwestern frontal system where it helped to enhance what already was heavy convective rainfall (details discussed on the tropical storms listserv previously).

The PV anomaly over the eastern Gulf of Mexico to the northwest of Cuba (it was in the process of forming 72 h earlier northeast of the Bahamas) is retreating westward in response to ridging on the poleward side of strengthening TC Dean to the south of Hispaniola.

0000 UTC 22Aug:

Remnant low-level vorticity from Erin, previously over OK 72 h earlier, can be tracked eastward to NC/SC where it was associated with a severe weather outbreak (mostly damaging winds). The Erin PV anomaly is last evident with confidence at 1200 UTC 20 Aug over the IL/IN/KY region. A 24 h gap in maps until 1200 UTC 21 Aug precludes tracking this feature and further for now.

The PV anomaly (cutoff cyclone) being "chased" to the NW by TC Dean is now located over northern Mexico near 27 N and 103 W while Dean is entering the Bay of Campeche.

0000 UTC 24Aug:

Dean low-level vorticity remnant is getting its "second wind" along the west coast of Mexiconear 21 N and 106 W while the PV anomaly "chased" westward across Mexico by Dean is situated over the eastern Pacific near 26 N and 117 W. The Dean low-level vorticity (PV anomaly) remnant is still beneath anticyclonic (cyclonic)deep-layer shear. One issue is whether downslope flow along the western slopes of the coastal western Mexico mountains contributed to vorticity growth and concentration in conjunction with vortex tube stretching.

0000 UTC 27Aug:

Dean low-level vorticity maximum moves NNW over the Gulf of CA, weakens and disappears. Tropical moisture associated with Dean is advected poleward to the east of the still alive and kicking (cold core) PV anomaly, now situated on the coast of southern CA, that played "tag" with Dean since it formed via a fracture from a PV tail east of the Bahamas on 0000 UTC16 Aug. Early morning rains in the PHX area (metars follow) on 25 Aug were indicative of the poleward moisture transport as were localized very heavy rains over interior regions of southern CA, southern NV and extreme northwestern AZ over the next 36 h as typified by metar reports from LAS (after the PHX metars).

KPHX 251151Z09006KT 10SM VCTS BKN090CB OVC130 29/18 A2989 RMK AO2PK WND

15027/1116 TSB07 SLP100 FRQ LTGCGIC VCVCTS MOV NW T02890178 10322 20283 53019=

KPHX 251251ZVRB05KT 5SM VCTS +RA FEW027 BKN090CB OVC130 27/19 A2993 RMK AO2

RAB03E18B40 SLP115 FRQ LTGCGIC OHD ANDVC VCTS SE MOV W CB DSNT SE-SW-W P0012 T02670194=

KPHX 251351Z20011KT 10SM TSRA FEW070 BKN095CB OVC130 25/23 A2995 RMK AO2

SLP122 FRQ LTGCGIC OHD AND VC TSOHD-SE-SW-W MOV W VIS LWR SW P0005 T02500233=

KPHX 251451Z00000KT 10SM -TSRA SCT060 BKN095CB OVC120 24/24 A2997 RMK AO2

SLP129 FRQ LTGCGIC OHD AND VC TS NW-NMOV NW P0007 60024 T02440239 51027=

KLAS 270556Z05003KT 10SM BKN140 BKN200 32/14 A2978 RMK AO2 SLP053 T03170139 10339 20311

51016 $=

KLAS 270656Z10009KT 10SM BKN095 BKN140 32/14 A2980 RMK AO2 SLP060 BKN095 V SCT T03170144

KLAS 270751Z05015G22KT 10SM VCTS -RA BKN095CB BKN140 31/12 A2980 RMK AO2 TSB51RAB51 OCNLLTGCG E-SE VCTS E-SE CB E-S P0000 403720283

KLAS 270756Z06016G22KT 10SM VCTS -RA BKN095CB BKN140 30/13 A2980 RMK AO2 TSB51RAB51

SLP060 OCNL LTGCG VC E-SE VCTS E-SE CBOHD P0000 T03000133 403720283 $=

KLAS 270803Z05015G22KT 10SM -TSRA FEW024 OVC090CB 29/16 A2981 RMK AO2 OCNL LTGCGCA E-S TSE-S AND OHD P0000 $=

KLAS 270756Z06016G22KT 10SM VCTS -RA BKN095CB BKN140 30/13 A2980=

KLAS 270856Z04012KT 10SM -TSRA FEW022 BKN041 BKN095CB 27/17 A2981 RMK AO2 SLP064 FRQ

LTGCGCA NE-S TS NE-S AND OHD MOV N P000260002 T02720167 51008 $=

KLAS 270915ZVRB05G15KT 5SM +TSRA FEW044 BKN085CB BKN110 25/17 A2986 RMK AO2 PRESRR VIS

E-S 1 1/2 CONS LTGCGCA OHD AND N-S TSOHD MOV N P0000 $=

KLAS 270956Z03006KT 3SM TSRA BKN023 BKN043 OVC090CB 24/18 A2984 RMK AO2 SLP078 VISE 2

CONS LTGCGCA S-NW TS NW-NE MOV NP0029 T02390178 $=

KLAS 271022Z32009KT 9SM -TSRA FEW012 BKN032 OVC110CB 23/19 A2983 RMK AO2 VISLWR W CONS LTGCGCA SW-N TS SW-N MOV N P0016$=

KLAS 271032Z04004KT 10SM VCTS FEW012 BKN032 OVC110CB 23/18 A2983 RMK AO2 RAE22 CONS

LTGCGCA VC SW-N VCTS SW-N MOVN P0016 $=

KLAS 271056Z28009KT 10SM VCTS -RA SCT090CB SCT120 BKN180 23/19 A2985 RMK AO2 SLP082

RAE22B50 CONS LTGCGCA VC S-N VCTS S-NMOV N P0016 T02330189 $=

KLAS 271156ZCOR 32005KT 10SM VCTS SCT085CB BKN120 23/18 A2984 RMK AO2 RAE01 SLP079 FRQLTGCGCA VC SW-N OCNL LTGCG DSNT E VCTS SW-NMOV

NP0000 60047 70047 T02330178 10317 20222 50011 $=

1200 UTC 27Aug:

Remnant PV anomaly has moved eastward to northern AZ and southern UT. Ridging ahead of it has reached the western Great Lakes.

ANE-SW oriented PV tail is crossing New England and will trigger weak cyclogenesis offshore. Upstream ridging over the Great Lakes is likely contributing to the southeastward movement of this PV tail.

1200 UTC 28Aug:

Remnant PV anomaly moves eastward and weakens. It is probably a stretch to stay that a figment of the PV anomaly (and/or my imagination) is located near 39 B and 95 W.

PV tail that had crossed New England 24 h earlier has now helped to spin up a low-level vorticity maximum at the southwestern end of the aforementioned PV tail near 38 N and 67 W. A second, reinforcing PV tail is crossing New England.

1200 UTC 29Aug:

The second PV tail across New England 24 h earlier is now oriented mostly W to E along 38 N and appears to be associated with low-level vorticity growth along 35 N from 67-72 W. The first PV tail was weakened and disappeared.

1200 UTC 30Aug:

PV maximum (manifest by higher pressure) that formed by fracture from the western end of the aforementioned PV tail is now embedded in anticyclonic deep-layer shear near 35 N and 70 W. Visible imagery for 1200 UTC 30 Aug provided by Zach Brown in a post with lots of good links to the tropical storms listserv (see below)shows an exposed low-level circulation center near 37 N and 70 W with deep convection to the SE. Steadily falling sea level pressure at this time seen in the attached meteogram from buoy 44004 near 38.5 Na and 70.4 W (NCDC buoy link is given below) is indicative of a developing system.

1200 UTC 31Aug:

A visible satellite image for this time from Zach's link shows a nice low-level but partially exposed circulation center near 38 N and 71 W with deep convection downshear to the NE. System looks like a weak TS. Increasing shear ahead of a deepening upper-level trough seen over the Great Lakes 24 h earlier completely exposes the low-level center by 2115 UTC as the strongest winds shift to the northeast quadrant of the storm (see attached 1612 UTC QuikScat image from Zach). I agree with Zach's inference that a post-season reanalysis might upgrade the East Coast system to a minimal TS.

Research Issues:

1. Document to what extent was the initial growth of low-level vorticity just to the south of western Cuba that eventually became associated with TS Erin may have been influenced by a westward-moving cold-core DT PV anomaly that formed via fracture from a PV tail over the western Atlantic?

2. Understand why Erin failed to become a full-fledged TS (let alone a TC) before landfall on the south Texas coast and what caused the increase in separation distance between the triggering PV anomaly that remained cold core and TS Erin as the storm made landfall on the Texas coast.

3. Determine what caused Erin to reorganize and apparently reintensify over western Texas and Oklahoma. This is an important story for another day and would be an ideal thesis topic for an interested student. See also related posts on this topic to the tropical storms listserv and map that contain assorted data from Erin after its landfall.

4. Investigate to what extent tropical moisture associated with Erin was able to be advected poleward and eastward ahead of the remnant DT PV anomaly that remained NW and then N of Erin after storm landfall in southern Texas. At issue is how much extra rainfall may have occurred along a WNW-ESE oriented front boundary from MN/WI/IA ESE to ILL/IN/OH in response to convective systems propagating along this boundary and feeding on any additional moisture from the former tropical system. Also of interest is whether the remnant Erin moisture contributed to a severe weather outbreak (mostly wind) through increased CAPE values over VA/NC. This is another good research problem for an interested student.

5. Decipher the relationship between TC Dean and the cold-core cutoff upper-level cyclone (PV anomaly) that remained to the NW of Deanas the stormmoved W/WNW from south of Hispaniola, across the Yucatan peninsula and Bay of Campeche, and Mexico. Was the observed WNW movement of the cutoff cyclone a consequence of strengthened southerly flow to the west of upper-level ridging induced by diabatically driven outflow from TC Dean?

6. Document the linkage between the poleward flux of tropical moisture from the remnants of Dean up the Gulf of CA and the aforementioned remnant cold-core upper-level cyclone and determine to what extent it contributed to the locally excessive rains in parts of southern CA, southern NV and western AZ.

7. Establish to what extent ridging over the Great Lakes on 28-29 Aug may have been an indirect result of the northeastward flux of heat and tropical moisture ahead of the remnant upper-level cold-core system that crossed the coast of southern CA near 0000 UTC 27 Aug and whether the likely associated downstream troughing over New England could have contributed to a possible weak (unnamed) TS development off the Midatlantic coast on 30-31 Aug.

Lance

To:tropical-storms@tstorms.org

Date: Sat, 01Sep 2007 00:35:44 -0400

From:hurricanewarn1@aol.com

Subject:[Tropical-storms] 96L, A Possible Candidate For A Post Season Upgrade

Hey all,

An interesting low pressure system paralleled the eastern seaboard of the United States over the past 2 days, and was particularly

Interesting over the past day. This low maintained a well defined surface circulation with organized convection from part of Thursday

and into part of Friday, as can be seen in these 2 visible satellite images.

http://i44.photobucket.com/albums/f34/abunter/96-4.jpg

http://i44.photobucket.com/albums/f34/abunter/96-5.jpg

I couldn't find a QUIKSCAT pass during the peak of the system unfortunately but, a pass as the system was losing convection revealed winds of 40 kt in the NE quadrant. I would suspect winds were higher during the peak organization of the system, and solidly minimal-moderate tropical storm force. Below is the QUIKSCAT pass and a visible satellite image of the system decaying into a tight swirl.

http://i44.photobucket.com/albums/f34/abunter/96-3.png

http://i44.photobucket.com/albums/f34/abunter/96-6.jpg

Also of note, 96L passed near Buoy 44004 while it was a tight swirl (well after the storm's peak), and a wind surge of up to 22 kt with a pressure drop down to1007 mb was observed.

http://i44.photobucket.com/albums/f34/abunter/96-1.png

As for the thermodynamic structure of the system, here’s some AMSU and FSU phase analysis charts. It looks warm core to me.

AMSU:

http://i44.photobucket.com/albums/f34/abunter/96-11.gif

http://i44.photobucket.com/albums/f34/abunter/96-10.gif

FSU phase analysis

http://i44.photobucket.com/albums/f34/abunter/96-8.png

http://i44.photobucket.com/albums/f34/abunter/96-9.png

Overall, a fairly intriguing system, one that should be considered for an upgrade to a tropical storm after the season. It reminds me a lot of the unnamed tropical storm last year off of Newfoundland actually: http://www.nhc.noaa.gov/pdf/TCR-AL502006_Unnamed.pdf

Sincerely,

Zach Brown

..............................................................

http://www.atmos.albany.edu/facstaff/rmctc/DTmaps/animSelect.php

(RonMcTaggart-Cowan's GFS animation builder)

Buoy 44004(Hotel): 38.5 N and 70.4 W

http://www.ndbc.noaa.gov/

http://maps.csc.noaa.gov/hurricanes/

Then "make tracks" to the "query storm track" sublink and you will have full access to plotting capability for historical Atlantic and eastern Pacific storms.