2012 Atlantic Hurricane Season Birdseye Discussion #64

By: NCHurricane2009 , 10:33 AM GMT on July 27, 2012

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...JULY 27 2012...6:35 AM EDT...
Atlantic tropics all clear as we head into the end of July.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0725Z-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...Survace frontal system and its upper trough over the central US and central Canada are merging with upper trough and frontal system in paragragph P2. Lowest surface pressure of this system...supported by eastern divergence of this upper trough...has risen from 999 mb to 1002 mb while traveling from the Great Lakes to New York state. Upper convergence behind this upper trough supports a 1020 mb surface ridge near NE Montana. Low-level westerly warm air advection south of this system has spread the SE US upper ridge into the west Alantic. This upper ridge is split into two cells (one over the W Atlantic...the other over the NW Gulf of Mexico) thanks to Caribbean upper vorticity mentioned in paragraph P8.

P2...Surface frontal system and upper trough over eastern Canada persists. 996 mb frontal cyclone south of Newfoundland...supported by eastern divergence of the upper trough...has slightly weakened to 997 mb while traveling northward across E Newfoundland. Cool air advection behind this cyclone has amplified the upper trough into the NW Atlantic. This cyclone has also driven its front southward such that its tail end is E of Bermuda...where a new 1015 mb depression appears to have formed from split flow upper divergence at the boundary between the upper trough mentioned in this paragraph and upper ridge mentioned in paragraph P1. However...upper convergence east of this upper ridge may cause this surface frontal depression to dissipate. On the other hand...if the upper ridge continues spreading eastward...it could overspread the frontal depression and enhance its upper outflow similar to a tropical system. But dry air beneath this upper ridge seen in the above thermo chart would inhibit tropical development.

P3...Surface frontal cyclone near the NE coast of Hudson Bay continues at 997 mb. It is still located beneath the axis of the upper trough mentioned in paragraph P2.

P4...Upper trough is still east of Greenland...and the system's trailing surface front had fizzled. The western end of the trailing front became absorbed into the east side of the systems mentioned in paragraphs P2 and P3. What was left of the eastern end of this trailing front was associated with a surface depression tracking south from the Azores...but that depression had dissipated thanks to upper convergence E of the North Atlantic upper ridge. The North Atlantic upper ridge remains amplified thanks to low-level warm air advection ahead of the systems in paragraphs P2 and P3. As this North Atlantic upper ridge stays amplified...so has the upper trough east of Greenland such that its south end still reaches the NW coast of Africa. Divergence east of this upper trough supports surface troughing over Spain...which has matured into a surface low and front over Spain and NW Africa.

P5...Cut-off upper vorticity south of Bermuda has pushed into the central Caribbean Sea from Hispaniola while retrograding around the upper ridge mentioned in paragraph P1.

P6...Atlantic surface ridge of 1017 to greater-than-1024 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 two upper ridge cells mentioned in paragraph P1...and convergence east of North Atlantic upper ridge (paragraph P4). 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...
P7...Inverted upper trough over Texas did not fully merge with the upper trough mentioned in paragraph P1. What is left is a cut-off upper vortex over south Texas.

P8...East Atlantic upper ridge persists. Upper vorticity west of the upper ridge...located in the Caribbean Sea...has retrograded NW about the upper ridge in paragraph P1...and into the SE Gulf of Mexico. In the wake of this upper vorticity...a south-central Caribbean upper ridge is building. However...the south-central Caribbean upper ridge is struggling to link with this east Atlantic upper ridge as upper vorticity in paragraph P5 digs southward. Also...upper vorticity remains embedded in this east Atlantic upper ridge...which has moved southwestward from the Canary Islands while retrograding about the amplified North Atlantic upper ridge in paragraph P4. This upper vorticity is splitting this east Atlantic upper ridge in half such that the upper vorticity has developed an inverted upper trough reflection west of the Cape Verde Islands...the reflection building where the east Atlantic upper ridge is splitting. Finally...inverted upper trough midway between the Cape Verdes and Lesser Antilles in the previous discussion is retrograding westward on south side of this east Atlantic upper ridge...and nearing the Lesser Antilles.

P9...Florida Panhandle surface trough has dissipated.

P10...Tropical wave in the western Caribbean in the previous discussion has moved into SE Mexico and Guatemala. It is largely suppressed by Caribbean upper vorticity mentioned in paragraph P8 that has moved into the SE Gulf of Mexico...although split flow divergence between the south-central Caribbean upper ridge (also mentioned in paragraph P8) and the upper vorticity is helping some of its t-storm activity located over the Gulf of Honduras.

P11...The tropical wave midway between the Cape Verde Islands and Lesser Antilles in the previous discussion is nearing the Lesser Antilles. The tropical wave remains suppressed by dry air mentioned in paragraph P6...and by inverted upper trough nearing the Lesser Antilles mentioned toward the end of paragraph P8.

P12...Tropical wave SW of the Cape Verde Islands in the previous discussion is now west of those islands. Although satellite animations still shows a surface low pressure spin...NHC TAFB in last 24 hrs has stopped analyzing this tropical wave as a tropical surface low. As expected during the previous discussion...tropical development has been stopped by dry air ingestion (source of dry air mentioned in paragraph P6). It was also speculated that SW-retrograding upper vorticity from Canary Islands (paragraph P8) would become vertically stacked with this tropical wave and suppress its upper outflow. This process has begun...with the development of an inverted upper trough reflection west of the Cape Verde Islands and over this tropical wave described in more detail in paragraph P8.

P13...Based on satellite imagery...the next tropical wave to roll off of Africa is entering the picture from the lower-right corner of the above atmo birdseye chart.

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2. NCHurricane2009
8:38 PM GMT on July 27, 2012
Quoting TropicalWxBlogger:
Good post. Keep up the good work on tropical weather!

Thanks...
Member Since: September 15, 2009 Posts: 540 Comments: 3713

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