2012 Atlantic Hurricane Season Birdseye Discussion #61
...JULY 24 2012...4:20 AM EDT...
Pop-up tropical disturbance over Florida has diminished (see paragraph P9). Frontal boundary low east-northeast of Bermuda has been introduced into the National Hurricane Center Tropical Weather Outlook...but I expect no tropical cyclone formation from this system (see paragraph P3 for details).
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0128Z-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...Surface frontal system and its supporting upper trough from SW Canada and the NW US in the previous discussion is now over Hudson Bay pushing quickly into eastern Canada. The associated 1004 mb surface frontal cyclone has intensified in the eastern divergence of the upper trough to 998 mb while now located in SE Canada. Upper convergence on the back side of this upper trough supports a surface 1016 mb ridge over Manitoba.
P2...Surface frontal system and its supporting upper trough over eastern Canada in the previous discussion has undergone complex changes in the last 24 hours. Its surface cyclone is now 997 mb on the NE coast of Hudson Bay while now becoming supported by the divergence east of the upper trough in paragraph P1. Meanwhile...its original upper trough has merged with the Ohio Valley upper trough in paragraph P3.
P3...Strong surface frontal cyclone southeast of Greenland has moved northeast out of the picture. Associated upper trough is still east of Greenland. Upper convergence behind this upper trough supports a 1018 mb ridge offshore of Nova Scotia. Upper anticyclone over the central US persists behind this system. Cold front trailing from the strong frontal cyclone has lost its frontal depression offshore of NC while the Ohio Valley upper trough has merged with the upper trough in paragraph P2. This merged upper trough is now in the NW Atlantic...with eastern divergence from this merger intensifying a 1015 mb frontal depression ENE of Bermuda that has been introduced into the National Hurricane Center Tropical Weather Outlook due to t-storm bands developing in its western semicircle. North Atlantic upper ridge in paragraph P7 is also just east of this frontal depression...which provides a means for this frontal depression to have tropical-like upper outflow in its eastern semicircle. Based on computer model runs...expect the NW Atlantic upper trough to merge with upper trough in paragraph P1...and all this upper troughing is going to significantly amplify due to cool air advection on the back side of this intensifying frontal depression. Warm air advection ahead of this same depression will significantly amplify the North Atlantic upper ridge...and eastern convergence of the amplifying upper ridge will intensify the surface ridge in paragraph P5. As the surface ridge intensifies to its east and upper troughing amplifies to the NW...this will coax the frontal depression into a rapid acceleration to the NE and quickly toward waters well below 26 deg C...which is why I do not expect tropical cyclone formation from this frontal depression. Even if cold de-stabilizing temps of upper troughing arrive over the frontal depression...I do not see enough time for transition into a tropical system in waters in the low 20s of deg C...as the depression will have little time over those water temps. I will write a special update later today if this situation changes.
P4...Cut-off upper vorticity south of Bermuda persists...wedged between the North Atlantic upper ridge (paragraphs P7 and P3)...east Atlantic upper ridge in paragraph P8....and warm core upper ridge over the Florida disturbance in paragraph P9. While this upper vorticity is enhancing the southern outflow of the special frontal depression in paragraph P3...still not expecting the frontal depression to become a tropical cyclone for reasons stated in paragraph P3.
P5...Atlantic surface ridge of 1020 to 1024 mb centers is supported by a few upper convergent sources while stretching from the SE US all the way toward western Europe....including convergence southeast of the central US upper anticyclone (paragraph P3)...convergence behind the Bermuda area upper vorticity in paragraph P4...and convergence SE of North Atlantic upper ridge (paragraphs P7 and P3). The west extent of this surface ridge has eroded some in the last 24 hours due to the frontal systems in paragraphs P2 and P3. In conjunction with the south side of the upper ridge in paragraph P8...south side of this surface ridge is helping to waft Africa desert dry air westward across the Atlantic tropics.
...TROPICAL BELT DISCUSSION...
P6...Upper ridge over Central America has re-amplified as the Caribbean upper vorticity mentioned in paragraph P8 weakens. Divergence from this upper ridge has enhanced t-storm activity over Central America.
P7...Inverted upper trough in the southern Gulf of Mexico remains amplified due to sharp definitions of warm core upper ridge of Florida disturbance to its east and central US upper anticyclone (paragraph P3) to its NW. Bermuda-area upper ridge has been spread eastward into the north Atlantic thanks to westerly warm air advection south of the frontal system in paragraph P3....and this North Atlantic upper ridge has been moved to the mid-latitudes discussion in that paragraph.
P8...East Atlantic upper ridge persists. Upper vorticity is still west of the upper ridge...located in the Caribbean Sea. Upper vorticity remains embedded in this upper ridge...originating over Canary Islands days ago and now over the Azores and waters SW. Warm air advection ahead of the strong frontal cyclone mentioned in paragraph P3 extends this upper ridge into western Europe.
P9...Surface tropical wave fragment over Florida has tracked NW into the NE Gulf of Mexico as expected...thanks to the slight western erosion of of the surface ridge described in paragraph P5. Under the outflow of the warm core upper ridge generated by its t-storms yesterday...the tropical wave fragment intensified into a weak 1018 mb surface low. Afterwards...it seems the 1018 mb low advected in the air properties to its west...including the increased upper vorticity of the inverted upper trough mentioned in paragraph P7. As the upper vorticity increased over the surface low...upper outflow directly above it shut off...which is why this disturbance has failed to develop into a tropical cyclone. Meanwhile...the east side of the surface low was able to produce a round of t-storms over the Florida peninsula and SW Atlantic waters while supported by the outflow of the warm core upper ridge. The surface low will continue to round the west side of the paragraph P5 surface ridge...so expect it to continue north into the SE US from the Florida Panhandle.
P10...Tropical wave in the eastern Caribbean Sea in the previous discussion is moving into the central Caribbean. Its t-storm activity is limited by the fact it is still below non-divergent uniform easterly flow...on the south side of the warm core upper ridge in paragraph P9 and north side of Caribbean upper vorticity mentioned in paragraph P8. However...there is an area of directional upper divergence west of Jamaica between the upper vorticity and upper ridge that may allow this tropical wave to see an increase in t-storms in the next 24 hours. It will then potentially enhance pre-existing t-storm activity over Central America mentioned in paragraph P6.
P11..A surprise in the southeast Caribbean and southern Lesser Antilles...as a well-organized cluster of cyclonically turning t-storms developed in the last 24 hours...associated with a tropical wave that had been poorly defined earlier. The intensification of this surface tropical wave is due to enhance poleward upper outflow on the west flank of the upper ridge in paragraph P8....but the t-storms have now rapidly decreased as it heads into an environment of less upper divergence...the same environment that is currently capping the amount of t-storms for the tropical wave in paragraph P10 above. Looking back in time...I estimate this tropical wave emerged from Africa shortly after July 18...based on an extensive area of debris clouds that was observed east of the tropical wave in paragraph P10 from July 19 to 20.
P12...The tropical wave west of the Cape Verde Islands has lost its low pressure spin on NHC TAFB maps in the last 24 hours. The above thermo birdseye chart continues to suggest dry air ingestion into the tropical wave's north half...the source of this dry air mentioned in paragraph P5. Still watching to see if tropical wave will move directly beneath the axis upper ridge in paragraph P8...which would enhance its upper outflow like it did for the tropical wave described in paragraph P11.
P13...A respectable tropical wave is rolling off the coast of Africa this early morning...feature a large mass of t-storms and cyclonic turning. Unlike the previous tropical waves...the surface pressure animations in computer models define this tropical wave better as it propagates westward. However...I am skeptical of tropical cyclone development from this wave too...as the recent string of tropical waves have failed to develop due to dry air currently mentioned in paragraph P5.