2012 Atlantic Hurricane Season Birdseye Discussion #48

By: NCHurricane2009 , 3:06 AM GMT on July 11, 2012

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...JULY 10 2012...11:05 PM EDT...
So far no signs of tropical development along frontal boundary...associated with deep-layered cyclone in Northwestern Atlantic (see paragraph P2).

I believe there is slight potential for a tropical disturbance in the eastern Gulf of Mexico beginning 48 hours from now. See paragraph P6 for details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1929Z-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...Upper ridge over North America has weakened due to cool air advection behind NW Atlantic cyclone in paragraph P2....except for the western US where warm air advection ahead of a frontal system pushing into western Canada is supporting a re-build of upper ridging. Westerly warm air advection south of the NW Atlantic cyclone has spread this upper ridge far eastward across much of the north Atlantic. Upper convergence on the south side of this upper ridge supported a surface ridge in the Gulf of Mexico that is presently weakening as explained in paragraph P6.

P2...Northwest Atlantic surface cyclone remains centered over eastern Canada with a diffuse surface center of 992 mb as of 1929Z. Now that the surface center has whirled beneath the less divergent core of its supporting longwave upper trough...expect the surface center to continue decaying. Upper convergence behind the longwave upper trough supports a 1022 mb surface ridge over the central US. Split flow upper divergence between the SW edge of the longwave upper trough and north edge of the upper ridge in paragraph P1 supports t-storms...a long surface front...and frontal depressions across the SE US...all trailing from the surface cyclone. If this trailing front and t-storm activity sags southward into the favorable low shear/enhanced outflow of the upper ridge in paragraph P1...then tropical development in the northwest Atlantic could be possible in the next days.

P3...Northeast Atlantic upper trough persists. Its eastern divergence supports a weak 1021 mb surface low north of the Canary Islands as of 1800Z.

P4...Open Atlantic surface ridge still has a strong center...1031 mb just west of the Azores as of 1800Z...which is supported by upper convergence on the back side of the NE Atlantic upper trough (paragraph P3). South side of this surface ridge is helping to waft Africa desert dry air westward across the Atlantic tropics.

...TROPICAL BELT DISCUSSION...
P5...Central America upper ridge has weakened due to loss of t-storm activity (and associated latent heat release) that supported it. Easterlies on the south side of this upper ridge diverge heavily with westerly flow going into the upper vorticity in paragraph P6. This upper divergence supports t-storm activity over the Panama area.

P6...Caribbean upper vorticity has elongated into a few features while wedged between the Central America upper ridge in paragraph P5...eastern Caribbean upper ridge in paragraph P7...and North America upper ridge in paragraph P1. This upper vorticity has an upper vortex in the central Caribbean. This upper vorticity also consists of an upper low in the southern Gulf of Mexico...and upper trough over the Bahamas...with split flow divergence at the boundary between these two eroding the Gulf surface ridge in paragraph P1...and supporting t-storms across Florida and eastern Gulf of Mexico. GFS computer model shows the southern Gulf upper low and Bahamas upper trough persisting...so I interpret that the favorable upper divergence between the two should persist. The tropical wave in paragraph P9 should arrive to this favorable upper divergence in the next 48 hours...so I now believe a tropical disturbance is possible in the eastern Gulf of Mexico by that time.

P7...Eastern Caribbean upper ridge persists.

P8...Expansive east Atlantic upper ridge has reversed to large-scale upper vorticity...an effect due to relatively lower pressures south of the upper ridge in paragraph P1 that has recently expanded across the north Atlantic. What is left of the east Atlantic upper ridge is toward the west coast of Africa...in relatively higher pressures south of the NE Atlantic upper trough (paragraph P3).

P9...Tropical wave crossing Puerto Rico in the previous discussion is now over Hispaniola and waters north. It is encountering unfavorable conditions thanks to westerly vertical shear from the Bahamas upper trough in paragraph P6...but divergence on the east side of this upper trough is allowing the north side of the tropical wave to produce t-storms NE of the Bahamas. See paragraph P6 for how this tropical wave may contribute to an eastern Gulf of Mexico disturbance beginning 48 hours from now.

P10...Tropical west of the Cape Verde Islands remains suppressed by dry air mentioned in paragraph P4..and is also suppressed by upper convergence directly beneath the new upper vorticity mentioned in paragraph P8.

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5. sunlinepr
6:13 AM GMT on July 11, 2012
Good info.... Thanks
Member Since: August 2, 2010 Posts: 21 Comments: 9882
4. allancalderini
4:05 AM GMT on July 11, 2012
Good job hope we get a little disturbance to track.
Member Since: October 15, 2011 Posts: 0 Comments: 4467
3. nigel20
4:02 AM GMT on July 11, 2012
Quoting NCHurricane2009:

If the east Caribbean upper ridge (paragraph P7) persists...and the tropical wave in paragraph P10 gets outflow from this upper ridge...then maybe the SAL (dry air) can be fought off and give the Leewards some rain. Otherwise...SAL will be king for quiet a few more days...

Thanks..hopefully they'll be able to get some relief pretty soon.
Member Since: November 6, 2010 Posts: 12 Comments: 8473
2. NCHurricane2009
3:41 AM GMT on July 11, 2012
Quoting nigel20:
Thanks NC! When will the leeward islands get some rain...SAL seems to be suppressing convection?

If the east Caribbean upper ridge (paragraph P7) persists...and the tropical wave in paragraph P10 gets outflow from this upper ridge...then maybe the SAL (dry air) can be fought off and give the Leewards some rain. Otherwise...SAL will be king for quiet a few more days...
Member Since: September 15, 2009 Posts: 539 Comments: 3712
1. nigel20
3:13 AM GMT on July 11, 2012
Thanks NC! When will the leeward islands get some rain...SAL seems to be suppressing convection?
Member Since: November 6, 2010 Posts: 12 Comments: 8473

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