2012 Atlantic Hurricane Season Birdseye Discussion #43
...JULY 5 2012...7:10 AM EDT...
Concerning latest information on eastern Caribbean tropical wave in special update #42A...see paragraph P11.
Disturbed weather offshore of the northeastern United States and north of Bermuda...also in special update #42A...has been upgraded to a special feature on this blog in case it surprises us. See the special feature section for more details on this situation.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0811Z-released HPC analysis.
In light blue is upper air analysis, 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 indicate surface lows, Hs indicate 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).
...SPECIAL FEATURE...NORTHWESTERN ATLANTIC DISTURBANCE...
This disturbance is currently north of Bermuda and east of the northeastern US coast...moving due east amongst westerly flow on the north side of surface ridges mentioned in paragraphs P1 and P5. As mentioned in special update #42A...this disturbance formed along the surface warm front of what is now the 1002 mb NE US cyclone mentioned in paragraph P1. Warm air advection from the 1002 mb cyclone amplified the eastern lobe of the upper ridge in paragraph P1 such that it aligned with the warm front and enhanced upper outflow similar to a tropical cyclone's structure. Recently...the warm front has been downgraded to a surface trough (suggesting more tropical characteristics in the area with air mass contrasts diminishing).
Looking ahead..conditions are expected to become less favorable as this disturbance continues eastward away from the 26 deg C Gulf stream waters. Moreover...the favorable lobe of upper ridging looks to get squeezed out as the NE US 1002 mb cyclone's upper trough merges with a west Atlantic upper trough (end of paragraph P2). But because the disturbance still has a good spin and abundant t-storm activity on satellite animations...it may suprise us by becoming upgraded to a short-lived tropical cyclone before then...if not at least an area of interest in the NHC Tropical Weather Outlook or an Invest on the NRL (Naval Research Laboratory) site. That is why I have upgraded it to a special feature on this blog.
P1...While moving eastward across the central North America upper ridge...southern Hudson Bay frontal system anchored by 998 mb center 24 hrs ago has arrived to the northeastern United States with a diffuse 1002 mb center...and its supporting upper trough follows behind. Convergence on the back side of this upper trough supports a 1013 to 1014 mb ridge over eastern Hudson Bay. This upper trough also left behind a cut-off upper low over the Tenessee valley 24 hrs ago which has since weakened to an upper trough in the midst of the strong central North America upper ridge. A second upper trough and frontal system from SW Canada is now over south-central Canada while continuing to zoom east across the north side of the central North America upper ridge. Upper convergence on the east side of this upper ridge is supporting the 1018 mb ridge in the eastern Gulf of Mexico...which extends to a 1022 mb center E of Bermuda.
P2...Complex frontal system covering the northern half of the Atlantic Ocean persists. A frontal cyclone and its supporting upper trough has made landfall in western Europe (marked as an extratropical low in the upper-right of the above charts). What is now a 1010 mb frontal cyclone speeding eastward to Europe was a diffuse cyclone over E Canada 24 hrs ago. It has left behind its supporting upper trough over the western Atlantic...carving out its own shortwave upper trough with cool air advection as it heads toward Europe. Meanwhile...the residual west Atlantic upper trough will be merging with the upper trough of the 1002 mb northeastern US cyclone mentioned in paragraph P1.
P3...Upper ridge over Greenland and the high seas south of Greenland is de-amplifying as it get squeezed out in between the 1010 mb cyclone's upper trough and western Atlantic upper trough...both upper troughs mentioned in paragraph P2 above.
P4...Cut-off upper vortex southwest of the Azores continues to shift westward while retrograding about the upper ridge in paragraph P3. The surface trough it once supported has moved westward while steered by strong surface ridge mentioned in paragraph P5. Surface trough is visible on satellite as a faint swirl of clouds.
P5...Open Atlantic surface ridge still has a strong center....currently just north of the Azores...which is supported by upper convergence on the back side of the upper troughs/surface frontal cyclones currently pushing into Europe (paragraph P2).
...TROPICAL BELT DISCUSSION...
P6...Inverted upper trough over the Bay of Campeche and western Gulf of Mexico is retrograding slowly west into Texas and NE Mexico while orbiting the strong central North America upper ridge mentioned in paragraph P1.
P7...Upper ridge over Central America is enhancing upper outflow for t-storm activity across the region. Surface convergence from a tropical wave (formerly Invest 97-L) is also be enhancing this activity. As mentioned here yesterday...it looks as though this system will shift westward into the eastern Pacific and potentially develop there.
P8...Central Caribbean upper vorticity has spilt off from western Atlantic upper trough (paragraph P2) after merging with it yesterday. Split is due to strength of central North America upper ridge. This upper vorticity has an upper vortex spinning over the east Bahamas and east Cuba.
P9...Eastern Caribbean upper anticyclone persists.
P10...Expansive east Atlantic upper ridge continues...featuring an anticyclonic center SE of the Azores. In conjunction with the surface ridge in paragraph P5...deep-layered easterly flow exists across much of the Atlantic tropics that is advecting African desert dry air (brown shading in the above thermo birdseye chart) westward. Inverted upper trough signatures on the south and east sides of this east Atlantic upper ridge continue.
P11...Tropical wave crossing the Lesser Antilles in the previous discussion is moving across the eastern Caribbean today...and this morning's 0600Z TAFB position places it across Puerto Rico. The upper outflow produced by the east Caribbean upper ridge (paragraph P9) has allowed the tropical wave to see a good increase in its t-storm activity in the past 24 hours. It also briefly became an area of interest in the NHC Tropical Weather Outlook thanks to gusty winds measured over the Virgin Islands. In the short-term...the t-storm activity of the tropical wave looks to move over Hispaniola (Haiti and the Domincan Republcic). After that...the tropical wave looks to get sheared by central Caribbean upper vorticity (paragraph P8)...which is why it is still not expected to develop.
P12...Strong tropical wave SE of the Cape Verde Islands in the previous discussion is now west of those islands this morning. This tropical wave is also in favorable low shear thanks to deep-layered easterly flow mentioned in paragaraph P10...but is rolling into the dry air also mentioned in paragraph P10...and therefore I do not expect it to develop in the next days.