2012 Atlantic Hurricane Season Birdseye Discussion #66
...JULY 29 2012...5:50 PM EDT...
Watching tropical disturbance in the eastern tropical Atlantic (see paragraph P9). This is the last chance of a July Atlantic tropical cyclone this year.
Of side note...if no Atlantic tropical cyclone develops before August 1...this will be the first July since 2009 with no July Atlantic tropical cyclone activity.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1332Z-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).
P1...Longwave upper trough regime persists across eastern North America...with low-level warm air advection ahead supporting a west Atlantic upper ridge...while another upper ridge builds behind over the SW US. Hudson Bay surface cyclone and north Canada upper trough are gradually shifting east. Convergence between this north Canada upper trough and SW US upper ridge supports a 1021 mb west US surface ridge...while a 1020 to 1021 mb surface ridge from the Great Lakes to east Canada is supported by upper convergence on the back side of this longwave upper trough regime. Accelerationally divergent westerly jet on north side of SW US upper ridge appears to support a disorganized 1009 to 1011 mb frontal depression near the Dakotas and Manitoba. Newfoundland frontal depression has moved NE to waters S of Greenland...and NE US frontal depression has moved to waters offshore of Massachusetts. S Greenland frontal depression intensified from 1006 to 1003 mb in last 24 hrs while taking advantage of eastern divergence of a shortwave upper trough impulse in the longwave.
P2...Upper trough east of Greenland is approaching western Europe. Divergence east of this upper trough supports surface troughing over Spain...marked with a 1012 mb low pressure center as of 1200Z NHC TAFB map. South end of upper trough is fracturing to the east of the W Atlantic upper ridge in paragraph P1. Fracture includes upper vortex just SE of the Azores...and shortwave upper troughs WNW of the Cape Verde Islands.
P3...Cut-off upper vorticity in the central Caribbean Sea consists of an upper vortex over Cuba and upper vortex just SW of Jamaica.
P4...Atlantic surface ridge of 1019 to 1025 mb centers is supported by a few upper convergent sources while stretching from the Gulf of Mexico/SE US to the waters offshore of west Europe....including convergence SE of the of the SW US and west Atlantic upper ridges in paragraph P1. In conjunction with the south side of the upper ridge in paragraph P6...south side of this surface ridge is helping to waft Africa desert dry air westward across the Atlantic tropics.
...TROPICAL BELT DISCUSSION...
P5...Texas inverted upper trough had dissipated.
P6...East tropical Atlantic upper ridge persists...spanning from west Africa to the east Caribbean. Upper vorticity west of the upper ridge...located in the Gulf of Mexico...is weakening to the south of the SW US upper ridge in paragraph P1. South-central Caribbean upper ridge continues enhancing Central America area t-storms...and struggles to link with this east Atlantic upper ridge due to upper vorticity in paragraph P3. Upper vorticity remains embedded in this east Atlantic upper ridge with a series of inverted upper troughs. Upper vortex just north of the Lesser Antilles is retrograding westward about W Atlantic upper ridge in paragraph P1...and inverted upper trough SW of the Cape Verde Islands is now midway between the Cape Verdes and Lesser Antilles. Yet another inverted upper trough has developed just SE of the Lesser Antilles (see paragraph P8 for details).
P7...Tropical wave in the eastern Caribbean remains suppressed by dry air as it heads into the central Caribbean. Source of dry air mentioned in paragraph P4.
P8...Tropical wave midway between the Cape Verde Islands and Lesser Antilles is now nearing the Lesser Antilles. Surface low pressure spin evident in past days had dissipated...but associated t-storm activity has increased. This is due to upper divergence on the west flank of inverted upper trough midway between Cape Verdes and Lesser Antilles (paragraph P6). Increase in t-storms is also due to upper ridge axis in paragraph P6 shifting southward over the tropical wave and enhancing its upper outflow. Recent shift in upper ridge axis is due to southward dig of upper fractures mentioned in paragraph P2. Latent heat release of t-storms is locally inflating the upper ridge axis...creating an inverted upper trough just SE of the Lesser Antilles which is a manifestation of relatively lower upper atmo pressures west of the latent-heat-release driven upper ridge inflation.
P9...Suspect tropical wave is marked with a 1011 mb ITCZ low southwest of the Cape Verde Islands. This feature is still not designated an official tropical wave in NHC tropical weather discussion. Easterly vertical shear over the tropical wave has diminished as the upper ridge axis in paragraph P6 has shifted southward over the tropical wave (shift due to southward dig of upper fractures mentioned in paragraph P2). This has allowed the low pressure spin of the tropical wave to receive enhanced upper outflow from the upper ridge axis...and this disturbance became intermittently organized. CMC and GFS computer models are beginning to suggest tropical cyclone formation from this system. Other than adjacent dry air mentioned in paragraph P4...this system is in favorable conditions. Coupled with developing computer model support...this system bears watching as it heads toward the Lesser Antilles this week.
P10...Satellite imagery suggests the next tropical wave is emerging from Africa (see lower-right corner of above atmo birdseye chart).