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2012 Atlantic Hurricane Season Birdseye Discussion #135
By: NCHurricane2009 , 7:45 AM GMT on October 17, 2012
...WEDNESDAY OCTOBER 17 2012...3:45 AM EDT...
Hurricane Rafael is pulling northeastward from Bermuda and should transition into a non-tropical cyclone in the next 24 hours. If transition is complete by the time of my next full discussion...it will no longer receive a special feature section on this blog. However...Rafael will be a strong non-tropical cyclone that provides impacts to the north Atlantic high seas. For now...refer to the Rafael special feature section below for details on this system.
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 0140Z-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...HURRICANE RAFAEL...
Rafael reached a peak intensity of 90 mph max winds...a little weaker than my intensity forecast in discussion #134...and a little stronger than my intensity forecast in discussion #134A. Rafael has weakened such that he is now at the exact intensity predicted for this time in previous discussion #134...so my intensity forecast in Figure 1 below is the same as in Figure 1 of discussion #134 except that I show a more gradual weakening rate. This is because Rafael has only weakened by 5 mph over the last several hours. Rafael is weakening from SW vertical shear and increasingly cooler waters he is tracking toward...but the weakening rate has been gradual due to supportive divergence on the east side of the paragraph P2 upper trough that will gradually transition Rafael to non-tropical. My forecast in Figure 1 is identical to the 11 PM EDT NHC forecast except that I disagree on the time to non-tropical status...which I predict to occur by 11 PM Wed while the NHC predicts this to occur 6 to 12 hours after that.
Track-wise...it initially appeared Rafeal was tracking to the right-of the previous track forecast during discussion #134...but has since returned and the previous NHC forecast track has done very well in the last 24 hours. As such...the NHC has essentially made no adjustments to the track forecast...and I continue to agree with it. Rafael is turning more eastward in his northward track as he has entered the westerlies on the south side of the 984 mb cyclone in paragraph P2. The GFS model shows Rafael maintaining the same relationship with the cyclone through the forecast period shown in Figure 1...so on the surface it would seem necessary to extrapolate the current NE track rather than bend it more eastward like the NHC shows. However...I believe the NHC's eastward bend will verify because Rafael will soon pass to the north of the 1028 mb ridge center in paragraph P3. In fact with Rafael being directly south of the aforementioned cyclone...he should be tracking straight east rather than NE...but the only reason their is still a northerly component to the track is from the 1028 mb ridge to the east. Once Rafael gets north of that ridge center...he will be able to turn more eastward on the south side of the cyclone.
Figure 1: My forecast generated for Hurricane Rafael at 1 AM EDT
Impact swath in Figure 1 is based on the 11 PM tropical storm wind radius...and extrapolating that along the forecast track.
P1...Next surface frontal system in the mid-latitude westerlies is entering the upper-left corner of the above atmo chart from western Canada and western US with a pair of upper troughs. The first upper trough has yet to enter the atmo chart..while the second is moving into central Canada and the central US. Upper ridge across Gulf of Mexico and western US in the previous discussion has de-amplified as the upper troughs push in...with what is left of this upper ridge over SE Mexico.
P2...Upper trough and surface frontal system over the eastern US in the previous discussion is now moving into the western Atlantic while absorbing W Caribbean upper trough fragment mentioned in paragraph P3 of the previous discussion. Western convergence of the upper trough supports dry air in SE Mexico and W Caribbean...as well as a 1014 mb ridge over the eastern US. Eastern divergence of the upper trough supports frontal depression that has intensified from 994 to 984 mb in the last 24 hrs while moving across SE Canada.
P3...Surface 982 mb gale near the south tip of Greenland in the previous discussion has moved ENE and weakened to less-than-1008 mb as its associated upper trough has moved eastward such that the gale is now suppressed by the western convergence of the upper trough. This same western convergence supports 1028 mb surface ridge that has moved from the western to the central Atlantic. Meanwhile...eastern divergence of the upper trough supports a new surface low in the upper-right corner of the above atmo chart located just offshore of the British Isles of Europe.
...TROPICAL BELT DISCUSSION...
P4...Remnants of Patty have dissipated in the vicinity of the Bahamas...Cuba...and SE Mexico.
P5...Large-sized central Atlantic upper ridge remains melded with warm core upper ridge of Rafael. The upper ridge over Rafael has become sheared-off from the storm by the upper trough in paragraph P2...and the upper ridge now extends into the SE half of the Caribbean in relatively higher pressures south of the paragraph P2 upper trough.
P6...1019 mb surface ridge in the eastern Atlantic in the previous discussion has become assimilated into the 1028 mb center of paragraph P3...and therefore is no longer an independent feature.
P7...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 while suppressed by a pocket of sinking dry air associated with the western convergence of the upper vortex...and or suppressed by westerly shear on the south side of the upper vortex. Meanwhile...the t-storm cluster continues persisting W of the Cape Verde Islands while enhanced by outflow from an E tropical Atlc upper ridge that persists in relatively higher pressures E of the upper vortex.
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.