2012 Atlantic Hurricane Season Birdseye Discussion #67
...JULY 31 2012...3:50 AM EDT...
Disturbance in eastern tropical Atlantic has been upgraded to Invest 99-L...but is slowly organizing (see paragraph P8).
Elsewhere...new frontal disturbance offshore of Carolinas showing no signs of tropical development (see end of paragraph P1). Both tropical waves currently in the Caribbean Sea have become more impressive...but neither are showing signs of tropical development (paragraphs P6 and P7).
Of side note...if no Atlantic tropical cyclone develops in the next 24 hours...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 1800Z, and the 1919Z-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).
...MID-LATITUDES DISCUSSION...
P1...Longwave upper trough regime across eastern North America is spreading into the high seas of the Atlantic...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 has diminished while its upper trough is in E Canada. Another upper trough is swinging in from Hudson Bay...supporting a new 1004 to 1006 mb frontal depression just south of Hudson Bay. Convergence between this longwave upper trough regime and SW US upper ridge supports a 1020 to 1018 mb west US surface ridge...while a 1020 mb surface ridge from NE US to Atlantic Canada is supported by upper convergence on the back sides of embedded shortwave upper troughs. Accelerationally divergent westerly jet on north side of SW US upper ridge appears to support a disorganized 1010 mb frontal depression over the central US. Frontal depression S of Greenland is heading ENE to Europe...and frontal depression offshore of Massachusetts is now offshore of Newfoundland. S Greenland frontal depression has weakened to 1010 mb without support of a shortwave upper trough. Finally...shortwave upper trough over SE US supports frontal depression activity along the coast of the Carolinas...which showed impressive t-storms ventilating into the W lobe of W Atlantic upper ridge. This activity is not as impressive this early morning...resembling more of a non-tropical system heading NE toward cooler waters and NE US shoreline.
P2...Upper trough east of Greenland has moved into Europe. It leaves behind fractures east of W Atlantic upper ridge...including upper vortex just SE of the Azores...and mid-ocean upper vortex. Divergence east of the upper vortex SE of the Azores supports surface troughing over Spain...marked with a surface low and trough as of 1800Z TAFB.
P3...Cut-off upper vorticity in the Caribbean Sea consists of an upper vortex over Cuba with upper trough extending to the southeast.
P4...Atlantic surface ridge of 1019 to 1022 mb centers is supported by a few upper convergent sources while stretching from the Gulf of Mexico to the waters offshore of west Europe....including convergence SE of the of the SW US and west Atlantic upper ridges in paragraph P1. South side of this surface ridge is helping to waft Africa desert dry air westward across the Atlantic tropics. However...this dry air appears to be reducing due to enhancement of tropical waves as described in paragraphs P5....P7....and P8. Within this surface ridge...a mid-ocean surface 1016 mb low has popped up with supportive upper divergence between mid-ocean upper vortex in paragraph P2 and W Atlantic upper ridge in paragraph P1. A 1022 mb low has popped up S of the Azores with supportive divergence between the two cut-off upper vortices mentioned in paragraph P2.
...TROPICAL BELT DISCUSSION...
P5...East tropical Atlantic upper ridge has shifted southward over the tropical waves in paragraphs P7 and P8. This shift is due to southward dig of upper fractures mentioned in paragraph P2. The tropical wave t-storm activity has locally inflated the upper ridge into cells of upper anticyclonic outflow. Upper vortex N of the Lesser Antilles...once embedded in this upper ridge...has tracked NW to waters SW of Bermuda while orbiting W Atlantic upper ridge in paragraph P1. Upper vorticity west of the upper ridge...located in the south 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 t-storms associated with the tropical wave in paragraph P6...and struggles to link with this east Atlantic upper ridge due to upper vorticity in paragraph P3.
P6...Tropical wave moving across central Caribbean is pushing into central America. It has seen a tremendous increase in t-storm activity in the last 24 hours thanks to boosted outflow from south-central Caribbean upper ridge in paragraph P5. The tropical wave is currently speeding westward away from the t-storm activity...and no signs of tropical cyclone development are occurring in this area. No current computer models are suggesting tropical development.
P7...Tropical wave nearing the Lesser Antilles has crossed the islands into the eastern Caribbean Sea. Associated t-storm activity continues to increase as it has established upper anticyclonic outflow as mentioned in paragraph P5. No signs of tropical cyclone development are occurring in this area. No current computer models are suggesting tropical development.
P8...Tropical wave southwest of the Cape Verde Islands has been upgraded to Invest 99-L. Its surface low pressure is marked at 1009 mb as of 1800Z NHC TAFB. This surface low and t-storms has favorable conditions thanks to established upper anticyclonic outflow as mentioned in paragraph P5. National Hurricane Center Outlook suggests 20% chance of tropical cyclone formation here in next 48 hours. The CMC model still shows a stronger tropical cyclone tracking more WNW toward northern Lesser Antilles and passing near or north of the Bahamas. The GFS model still shows a weaker tropical cyclone tracking more W into the Lesser Antilles and Caribbean. The faster this develops...the more deep-layered the system becomes such that SW-retrograding upper vorticity (paragraph P2) pulls this system more north (like the CMC model). I am leaning toward a more southern solution straight toward the Lesser Antilles (like the GFS) due to the rather slow rate of organization of the disturbance currently observed. I am not yet upgrading this to a special feature on this blog until the disturbance shows a more imminent trend of becoming a tropical cyclone.
P9...Based on satellite...tropical wave rolling off of Africa in the previous discussion I now estimate to be south of the Cape Verde Islands. This tropical wave has not yet been acknowledged by NHC TAFB. Satellite imagery suggests the tropical wave is under northerly shear thanks to upper anticyclonic outflow of neighboring wave in paragraph P8.
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