2012 Atlantic Hurricane Season Birdseye Discussion #108
...SEPTEMBER 16 2012...4:11 AM EDT...
Hurricane Nadine continues to truck quickly eastward in the last 24 hours. The tropical cyclone will be south of the Azores by 5 days out...so interests in the Azores should monitor the progress of this system until it is clear if the tropical cyclone will move toward or away from the islands. See Nadine special feature section below for further details.
The tropical wave approaching the Lesser Antilles and Caribbean Sea has been upgraded to Invest 92-L in the last 24 hours. Due to potential for more favorable upper winds in the next days...I have upgraded this to a special feature section on this blog. See the second special feature section below for details.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0127Z-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 NADINE...
Nadine has continued accelerating eastward toward the paragraph P5 deep-layer vortex in the last 24 hours...and her eastward motion is still slightly faster than the previous forecasts even though those forecasts upped the pace of the eastward track. Therefore my updated forecast in Figure 1 is a rightward adjustment from the previous in all forecast points to account for the initial faster-than-expected eastward motion.
I support an increasingly slower eastward progression after 24 hours due to resistance from a NE Atlantic low-level ridge...which is currently the 1026 mb ridge entering the Atlantic high seas (paragraph P2) expected to zoom eastward to that location. This slow down allows the paragraph P5 deep-layered vortex to slip away from Nadine...leaving Nadine trapped in a narrowing gap between the paragraph P6 low-level ridge to the south and NE Atlantic low-level ridge. As the two low-level ridges bridge to the east of Nadine...I support a northward turn between 48 and 72 hrs. In between 72 and 84 hrs...I believe Nadine will wiggle left toward a low-level ridge weakness associated with what is now the 1008 mb low in paragraph P2. As the weakness passes by to the north between 84 and 96 hrs...I believe Nadine will then wiggle back rightward while trying to link with that weakness. However...it looks as though Nadine will fail to link with this weakness...which I predict will cause her to loop clockwise in track between 96 and 120 hrs as she comes under the influence of an impressive deep-layered ridge coming in from the NW that develops ahead of the paragraph P1 upper trough.
Figure 1: My forecast for Hurricane Nadine created this morning.
Intensity-wise for the next 24 hours...I weaken Nadine faster than the 11 PM EDT NHC forecast shows...as I expect her currently quick eastward pace will move her into unfavorable upper convergence and zonal shearing upper westerly flow on the SW quad of the paragraph P5 deep-layer vortex. The slow down in track between 24 and 48 hours should allow the less shearing (more favorable) NW Atlantic upper ridge wave ahead of what is now the paragraph P2 1008 mb low to catch up to and overspread Nadine...so I flatten the weakening rate during this time. I accelerate the weakening rate by 72 to 120 hrs as Nadine's forecast erratic track straddles the marginally favorable 26 deg C sea-surface temp isotherm...and experiences unfavorable SW vertical shear delivered by shortwave upper trough associated with the aforementioned 1008 mb low.
The impact swath in Figure 1 is initialized based on the 11 PM EDT NHC tropical storm wind radius...which I lean rightward with respect to the storm track by 72 to 120 hrs to account for a forecasted increase in SW vertical shear for that timeframe. The swath is also shrunken to represent a weakening Nadine in the latter part of the forecast.
...SPECIAL FEATURE...TROPICAL WAVE INVEST 92-L...
The tropical wave approaching the Lesser Antilles and Caribbean Sea has developed a 1010 mb low pressure spin and become more vigorous in the last 24 hours due to split flow upper divergence on the SW quad of paragraph P7 central Atlantic upper ridge cell. Computer models insist that the eastern Caribbean upper trough (paragraph P4 and P7) would continue to retrograde westward as to allow the SW quad of the central Atlantic upper ridge cell to split off into a favorable shear-reducing and outflow-enhancing upper anticyclone directly over this tropical wave. Moreover...model runs suggest this favorable upper anticyclone becoming enhanced by warm air advection ahead of what is now the paragraph P1 frontal system as this tropical wave crosses the Caribbean Sea. Therefore...interests in the Caribbean should monitor this tropical wave over the next days. However...development could be obstructed if the tropical wave gets too close to the less favorable retrograding east Caribbean upper trough...or later on gets too close to what is forecast by models to be a highly-amplified upper trough associated with the paragraph P1 frontal system.
...MID-LATITUDES DISCUSSION...
P1...Next upper trough and surface frontal system in mid-latitude westerlies is entering the upper-left corner of the above birdseye charts from the NW US and western Canada.
P2...Cut-off upper vortex over the SW US has weakened into an upper trough...but its eastern divergence still supports a 1017 mb frontal low currently over northern Mississippi. Shortwave upper trough has moved from central to eastern Canada whose eastern divergence supports a 1008 mb frontal low moving into SE Canada and whose western convergence supports a 1024 mb low-level ridge across the eastern US. Warm air advection ahead of the 1008 mb low supports a NW Atlantic upper ridge wave...and this 1008 mb system is absorbing the western Atlantic low pressure system in paragraph P3. Shortwave upper trough across Greenland is sliding eastward toward Europe...with its western convergence supporting a 1026 mb low-level ridge moving into the Atlantic high seas from Atlantic Canada.
P3...Cut-off upper vortex over the W Atlantic has weakened into an upper trough whose eastern divergence supports a broad area of low surface pressures that has consolidated into a 1007 mb frontal low. This 1007 mb system however will soon merge with the 1008 mb system in paragraph P2. Cut-off upper vortex in the Gulf of Mexico has weakened into an upper trough.
P4...Cut-off upper vorticity in the open Atlantic and eastern Caribbean has been moved into paragraph P7 of the tropical belt discussion.
P5...Deep-layered vortex persists south of the Azores...with the shortwave upper trough and associated surface low (now 1007 mb) that entered the west half of this system yesterday becoming the dominant feature of this system. Long-lasting remnant low of Isaac has been absorbed by the east half of the 1007 mb low in the last 24 hours.
P6...Eastern Atlantic surface ridge...currently with a 1018 mb center... persists with support from eastern convergence of the paragraph P7 central Atlantic upper ridge cell.
...TROPICAL BELT DISCUSSION...
P7...Upper ridging across the tropical Atlantic persists. The Caribbean to central Atlantic upper ridge cell has split into two cells separated by an eastern Caribbean upper trough (paragraph P4). The strength of the central Atlantic upper ridge cell...in part due to the latent heat release of Hurricane Nadine...has caused a portion of the paragraph P5 deep-layer vortex to fracture into a separate upper vortex WNW of the Cape Verde Islands. Remainder of the upper ridging is located toward west Africa in relatively higher pressures SE of this new upper vortex.
P8...The tropical wave approaching the Lesser Antilles in the previous discussion has been upgraded to disturbance Invest 92-L...and has been moved into the Invest 92-L special feature section above.
P9...The suspect tropical wave south of the Cape Verde Islands in the previous discussion has been added into the NHC TAFB maps during the last 24 hours.
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