2012 Atlantic Hurricane Season Birdseye Discussion #24
...JUNE 10 2012...4:37 PM EDT...
After the unusual pre-season tropical activity in the Atlantic...prospecting for new activity in the latter part of June.
The unusual pre-season activity appears associated with the equally unusual "loopy" jet stream (with high amplitude upper troughs and ridges) seen this year. Every instance of pre-season activity was associated with cut-off upper vortices left behind by the loopy jet stream. Divergence on the periphery of the cut-off upper vortex triggers a surface cyclone...the shear reducing when the surface cyclone aligns with the upper vortex. Cold temps of the upper vortex de-stabilizes the atmosphere for t-storms and tropical development of the surface cyclone...in some cases above waters less than 26 deg C. For example...see the following statements made earlier on the blog this year concerning how cut-off upper vortices triggered subtropical/tropical development:
Discussion #1...4th and 5th paragraphs of west-to-east discussion...for prelude to Invest 91-L
Discussion #2...4th 5th and 6th paragraphs of west-to-east discussion...for prelude to Invest 91-L
Discussion #4...5th and 6th paragraphs of Open Atlantic Waters Discussion...for prelude to Invest 91-L
Discussion #10...special feature section...for Invest 92-L
Discussion #12...1st special feature section...for prelude to Tropical Storm Alberto
Discussion #17...Special feature section....for Tropical Storm Beryl
Looking ahead...here are some prospects for Atlantic tropical activity in the latter part of June. None of these propsects appear imminent at this time.
Concerning the mid-latitudes...numerical models (like GFS) had been developing an impressive cut-off upper low for June 13 to 15 during discussion #22..then backed of developing a cut-off upper low during discussion #23. The cut-off upper low was slated to develop from the weather system mentioned in paragraph P2 of today's discussion. Numerical models have now re-instated the development of this cut-off upper low...which is a merger of the SW-NE upper trough axis in paragraph P2 and upper vortex in paragraph P3. I believe there is a slight chance of a NW Atlantic subtropical cyclone from the forecasted cut-off upper low beginning June 13...see last sentences of paragraph P3 for further details.
From forecast surface maps generated by numerical models...it seems the 1009 mb Gulf coast low (paragraphs P1 and P2) will translate across the SE US and into the west Atlantic by June 15 and onwards. This system may merge with cold front of frontal cyclone currently moving in from west coast of North America (paragraph P1). Or alternatively...I believe there is a slight chance it could thrive under the upstream upper ridge (mentioned at end of paragraph P1) and become a W Atlantic tropical cyclone.
Concerning the tropical belt...computer models began flaring Caribbean upper ridging (paragraph P6 below) and developing a tropical cyclone beneath it (days after June 15)....for example see intro section of previous discussion #23. The GFS model is not displaying this solution as aggressively today...but we will be on the lookout as we get closer to this timeframe.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1329Z-released HPC analysis.
In light blue is upper air anlaysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.
In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicating surface lows, Hs indicating surface highs.
...THERMODYNAMICS BIRDSEYE CHART...
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.
Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).
P1...Surface frontal cyclone in SW Canada (in previous discussion #23) has been absorbed by a second cyclone moving into the west coast of North America. This second cyclone's center is not yet in the scope of the above charts...but its associated upper trough is now in the western US. Remnant upper trough once associated with the absorbed cyclone is now over the central US while absorbing a south Texas cut-off upper low (origins of cut-off upper low mentioned in previous discussion #23). Divergence E of this central US upper trough has been supporting heavy weather over the stalled SE US front mentioned in paragraph P2 below. This persistent heavy weather has caused flooding along parts of the US Gulf coast. Stalled SE US front has transitioned to a 1009 mb coastal Louisiana low supported by the central US upper trough...which unfortunately means heavy weather will persist along parts of the US Gulf coast. Finally...the upper ridge associated with warm air advection ahead of this complex weather system is now over the eastern US...and the upper ridge's eastern convergence supports surface ridge centers of 1020 mb in West Virginia...1021 mb near Bermuda...1020 mb over the NE US...and 1023 mb over SE Canada.
P2...Longwave upper trough in the western Atlantic consisted of an SW-NE-tilted axis and upper vortex over Atlantic Canada in previous discussion #23. Its SW-NE axis has now merged with a relatively-new frontal system covered in paragraph P3...and the upper vortex is now just SE of Greenland. The upper vortex featured a mature 996 mb surface cyclone in discussion #23...which has now weakened to 1011 mb in the above charts (while suffering from a lack of divergence beneath the upper vortex). At the surface...this system consisted of a long stalled front reaching into the SE US. This long stalled front no longer belongs with this system. One fragment is now a 1009 mb Gulf coast low mentioned in paragraph P1 above. Another fragment belongs to a new 1010 mb low mentioned in paragraph P3 below.
P3...Although not mentioned in previous discussions...a new frontal system has been emerging over Canada's Hudson Bay over the last days. Frontal system at the surface now consists of a 1011 mb cyclone & cold front pushing into the NW Atlantic...supported by divergence at the NE periphery of an upper vortex. Accelerational divergence SE of this upper vortex also supports a new 1010 mb frontal low in the central Atlantic. This new upper vortex has been spinning up in relatively low pressures between the upper ridge mentioned in paragraph P1 above and upper ridge in paragraph P5 below. This new upper vortex has also absorbed the SW-NE titled upper trough axis mentioned in paragraph P2 above. Upper vortex is expected to push SE across the NW Atlantic (above 23 to 24 deg C water) and amplify while the adjacent upper ridge in paragraph P1 amplifies to its west. I believe there is a slight chance that this upper vortex may be cold enough for subtropical cyclone development at the surface despite water temps below 26 deg C...during the June 13 to 15 timeframe later this week.
P4...Longwave upper trough regime across the entire high seas of the Atlantic is replaced by relatively-new upper anticyclone in the above birdseye charts...located S of the Azores...and caused by warm air advection ahead of system in paragraph P2. Surface 1025 mb Atlantic ridge in this area is now 1030 mb and vertically stacked with this upper anticyclone...creating a deep-layered anticyclone. In previous discussion #23 paragraph P3...what was left of the old upper trough regime was a cut-off upper trough in the central Caribbean...cut-off upper low midway between Lesser Antilles and Azores...and cut-off upper trough over over the Cape Verde Islands. All of these cut-off features are now a single east-west upper trough from the Caribbean Sea to Cape Verde Islands. This east-west upper trough will be moved to the tropical belt section of future discussions.
P5...Full-fledged and anomalous upper anticyclone over the east coast of Canada (paragraph P4 of previous discussion #23) has weakened to an upper ridge. Its eastern convergence supports a 1027 mb ridge S of Greenland.
...TROPICAL BELT DISCUSSION...
P6...Long-lived Caribbean upper ridging persists...currently forked in half by east-west upper trough mentioned towards the end of paragraph P4 above. The northern half is an upper anticyclone over Cuba...the southern half is an upper anticyclone N of Panama.
P7...Upper ridge in E tropical Atlantic has been pushed SE by east-west upper trough mentioned towards the end of paragraph P4. We had been talking about how the south side of this upper ridge...in conjunction with the south side of deep-layered anticyclone in paragraph P4...was wafting in dry air from Africa's desert. The more SE position of the E tropical Atlantic upper ridge has increased outflow over the area such that rising motion below this outflow has re-moistened the air. What's left of that dry air is in the east half of the Caribbean and central tropical Atlantic (using today's thermodynamics birdseye chart).
P8...Tropical wave WSW of Cape Verde Islands in discussion #23 has been moving west and is nearing the Lesser Antilles this afternoon. Currently...this tropical wave is inactive while suppressed by dry air (mentioned in last sentence of paragraph P7 above) and westerly vertical shear south of the east-west upper trough (mentioned towards the end of paragraph P4 above).
P9...Tropical wave has been added to NHC TAFB analyses (and likewise added into lower-right corner of the above charts) while emerging from west Africa. While it is entering the moistening air beneath the ridge of paragraph P7...it is experiencing unfavorable westerly vertical shear on the NE side of that same upper ridge.