2012 Atlantic Hurricane Season Birdseye Discussion #60
...JULY 23 2012...12:30 AM EDT...
Tropical wave that recently emerged from Africa no longer can develop in the short-term due to dry air ingestion (see paragraph P11). Disturbed weather in northern Gulf of Mexico...near Louisiana and Mississippi...has dissipated (paragraph P7).
A pop-up and strong tropical disturbance with tropical cyclone formation potential has developed over the western Bahamas and Florida. See special feature section for further details.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1925Z-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...TROPICAL WAVE DISTURBANCE...
A strong tropical disturbance over the west Bahamas and Florida...associated with the northern fracture of the tropical wave in paragraph P9...has rapidly developed during the last 24 hours. Special update #59A mentioned that the north fracture of the tropical wave found a very favorable upper divergence regime between the Caribbean upper vorticity (paragraph P8) and SW lobe of the east Atlantic upper ridge (also in paragraph P8). Special update #59B mentioned that the latent heat release of the t-storms has allowed the disturbance to develop a warm core upper anticyclonic ridge for good upper outflow. Therefore...the only unfavorable factor for development is high surface pressures associated with the surface ridge in paragraph P5. Miami obs reported 1021 mb at update #59A...down to 1019 mb at update #59B...and now back up to 1020 mb as of this writing. Key West has reported a 1018 mb pressure slowly rising to 1019 mb from update #59A to now. Mid-level pressure drops have been much more pronounced with the CIMSS 850 mb vorticity product locking on to an increase in the disturabance's mid-level vorticity...and a mid-level low pressure spin evident on satellite/radar over the south tip of Florida moving NW into the Gulf of Mexico. With a recent decrease in t-storm activity and the pressure drops only in the mid-levels...chances have just decreased (but not yet disappeared) for tropical cyclone formation...so this maybe the first and last time this disturbance gets a special feature section on this blog.
Paragraph P5 in the tropical belt discussion mentions erosion of the west end of the Atlantic surface ridge...which is why this disturbance is expected to continue NW into the NE Gulf of Mexico. This ridge erosion may allow for surface pressure drops needed for tropical cyclone formation. Regardless of development or not...gusty winds...heavy rains...and t-storms have already been reported across the west Bahamas and Florida...and the graphic in special update #59B shows the expected track of this weather thru Tuesday July 24 based on the forecast NW track.
P1...Next surface frontal system and its supporting upper trough in the mid-latitudes has pushed in from SW Canada and the NW US. It has a 1004 mb surface frontal cyclone over Manitoba marked in the above atmo birdseye chart.
P2...Surface frontal system and its supporting upper trough over central Canada has pushed into eastern Canada. Upper convergence on the west side of the upper trough supports a 1018 mb ridge over the Great Lakes. Upper divergence on the east side of the upper trough supports a pre-frontal surface trough over Newfoundland marked in the 1925Z HPC analysis. Warm air advection ahead of this frontal system supports an upper ridge moving into the Atlantic high seas toward Greenland.
P3...Strong deep-layered 966 mb frontal cyclone southeast of Greenland has moved northeast while weakening beneath its less divergent parent upper vortex. The parent upper vortex has weakened into an upper trough east of Greenland. Upper convergence behind this upper trough supports a 1022 mb ridge offshore of Nova Scotia. Upper anticyclone over the central US persists behind this system. Cold front trailing from the 966 mb cyclone has a frontal depression that has moved offshore from North Carolina while its supporting upper trough is still over the Ohio Valley. Convergence on the back side of the Ohio Valley upper trough supports a 1023 mb ridge over West Virginia. There are also a few North Atlantic frontal depressions along this trailing front...supported by divergence between northerlies flowing around the Bermuda-area upper ridge (paragraph P7) and westerlies flowing into upper trough east of Greenland.
P4...Cut-off upper vorticity south of Bermuda persists...wedged between the Bermuda-area upper ridge in paragraph P7...east Atlantic upper ridge in paragraph P8....and newly-formed warm core upper ridge over the disturbance in the special feature section.
P5...Atlantic surface ridge of 1020 to 1026 mb centers is supported by a few upper convergent sources while strecthing from the SW US all the way toward western Europe....including convergence south of the central US upper anticyclone (paragraph P3)...convergence behind the Bermuda area upper vorticity in paragraph P4...and convergence SE of Bermuda-area upper ridge which is being spread eastward into the north Atlantic (paragraph P7). The west extent of this surface ridge may become eroded by the tailings of the frontal systems in paragraphs P1...P2...and P3...which is why the disturbance in the special feature section should track NW into the NE Gulf of Mexico. 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 remains de-amplified into a strong westerly jet as the Caribbean upper vorticity mentioned in paragraph P8 dominates. This upper ridge has an anticyclonic center in the eastern Pacific whose divergence is enhancing the tropical wave in paragraph P9 as it moves into the eastern Pacific.
P7...Upper vorticity in the southern Gulf of Mexico has transitioned into an amplifying inverted upper trough across the Gulf...trapped between the warm core upper ridge of special feature disturbance to its east and central US upper anticyclone (paragraph P3) to its NW. The inverted upper trough's amplfication is due to the amplification of warm core upper ridge assocaited with the special feature disturbance to its east. 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. Northern Gulf t-storm activity near the MS/LA area has dissipated...and the surface trough of this disturbed weather has merged with a surface trough over the SE US...a breakage of the trailing cold front mentioned in paragraph P3.
P8...East Atlantic upper ridge persists. Upper vorticity is still west of the upper ridge...located across the Caribbean Sea. This east Atlantic upper ridge remains split into three cells thanks to embedded upper vorticity originating from Canary Islands and now partially over the Azores. The northern cell is moving into west Europe while associated with warm air advection ahead of the strong frontal cyclone mentioned in paragraph P3...the SW cell has an anticylonic center just N of the Lesser Antilles...and the SE cell is located toward Africa.
P9...Tropical wave pushing into central America/SE Mexico in the previous discussion has moved into the eastern Pacific...where the anticyclonic center of upper ridge in paragrah P6 is enhancing it. Westerly jet also mentioned in paragraph P6 looks directionally divergent based on the 200 mb wind barbs shown in the above atmo birdseye chart...this divergence supporting persistent t-storms over Central America and east of this tropical wave. Today...it is now apparent the tropical wave left behind a north fracture tracking across the west Bahamas and Florida. This north fracture contributed to a rapidly developing tropical disturbance as described in the above special feature section. See the special feature section for further details.
P10...Tropical wave approaching crossing the Lesser Antilles in the previous discussion is now in the eastern Caribbean Sea. Its t-storm activity is limited by the fact it is still below non-divergent uniform easterly flow on the southwest side of the upper ridge in paragraph P8.
P11...The tropical wave (with t-storms and low pressure spin) over the Cape Verde Islands in the previous discussion is now just west of those islands. Low pressure spin is analyzed at 1014 mb per 1800Z NHC TAFB map. Satellite shows a decrease in t-storm activity across the north half of the tropical wave as it ingests dry air (mentioned in paragraph P5)...so chances for this wave's development have decreased for the short term. However...still watching to see if tropical wave will move directly beneath the SE cell of the upper ridge in paragraph P8. If this were to occurr...the cell directly overhead and upper vorticity to the northwest (also mentioned in paragraph P8) would enhance the upper outflow of this tropical wave.