2012 Atlantic Hurricane Season Birdseye Discussion #136
...THURSDAY OCTOBER 18 2012...3:55 AM EDT...
Hurricane Rafael becomes extratropical (non-tropical) within the last 24 hours while accelerating east-northeast into the north Atlantic high seas. Although no longer a special feature on this blog...non-tropical Rafael is producing heavy rains...high winds...and rough seas...and therefore remains a marine threat. See paragraph P2 for statement on non-tropical Rafael.
An outage persists with GOES-E satellite imagery in the last several days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0130Z-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...Next surface frontal system in the mid-latitude westerlies continues marching eastward across North America with a pair of upper troughs. The first upper trough has entered from the top-left of the atmo chart while highly amplified with an embedded upper vortex. Strong convergence on the west side of the upper trough supports building surface ridge across the western US...while strong divergence on the east side of the upper trough is driving a strong frontal cyclone of 983 mb centered near the NW corner of Minnesota. Low-level southerlies ahead of the cyclone are in directional shear with respect to upper-level westerlies. The shear (along with instability) is supporting severe weather and tornadoes across Mississippi this early morning (vist www.nws.noaa.gov for any severe weather watches or warnings that may be required for this system across the southeast US over the next 24 hours). Second upper trough has moved from the central to the eastern US in the last 24 hrs..and its eastern divergence is producing cloudiness just offshore of the eastern US. Meanwhile...upper ridge persists across SE Mexico in relatively higher pressures south of both upper troughs.
P2...Upper trough and surface frontal system continues advancing into the western Atlantic. Western convergence of the upper trough supports 1015 to 1016 mb ridge over eastern Canada and offshore of SE US. Eastern divergence of the upper trough supports 989 mb frontal depression that has moved offshore from eastern Canada and headed for southern Greenland. Surface cold front of this depression has overspread former Hurricane Rafael in the last 24 hours as he accelerates ENE into the north Atlantic high seas. Eastern divergence of this upper trough also supports Rafael...so expect Rafael to only slowly weaken over the next several hours. Therefore...vigorous ex-Rafael remains a marine threat. Cold front in which Rafael is embedded extends toward the western Caribbean and western Cuba...where it leaves behind a pair of surface troughs.
P3...Upper trough continues advancing away from Greenland while continuing east across the NE Atlantic. Western convergence of the upper trough supports 1028 mb surface ridge that is moving from the central to the eastern Atlantic. Meanwhile...eastern divergence of the upper trough supports relatively new surface frontal low that has entered Europe from the British Isles. Cold front extending from the surface low extends to northern Canary Islands.
...TROPICAL BELT DISCUSSION...
P4...Large-sized central Atlantic upper ridge continues to extend into the SE half of the Caribbean Sea.
P5...In the tropical Atlantic east of the Lesser Antilles...cut-off upper vortex persists. Pair of tropical waves in the vicinity in the previous discussion are moving toward the Lesser Antilles. The eastern of the two waves is suppressed by a pocket of sinking dry air associated with the western convergence of the upper vortex...and suppressed by westerly shear on the south side of the upper vortex. The western of the two waves is crossing the southern Lesser Antilles while escaping the oppressive effects of the upper vortex...but is now suppressed by northerly shear from the paragraph P4 upper ridge. However...this western wave will enter a less hostile environment as it moves closer to the upper ridge axis...and it remains to be seen if the wave interacts with the favorable upper outflow of the upper ridge (their is computer model support for a broad Caribbean tropical low by 144 hours...but I am not yet sure if it is associated with this wave). Meanwhile...E tropical Atlc upper ridge and scattered t-storms (supported by outflow of the upper ridge) persists in relatively higher pressures E of the upper vortex.