2012 Atlantic Hurricane Season Birdseye Discussion #132

By: NCHurricane2009 , 11:42 PM GMT on October 13, 2012

...SATURDAY OCTOBER 13 2012...7:45 PM EDT...
In the last 36 hours...Patty has dissipated as a tropical cyclone just north of the eastern Bahamas. See paragraph P4 for statement on the remnant of Patty.

Strong tropical wave Invest 98-L has strengthened into Tropical Storm Rafael during the last 36 hours while moving northwest and northward across the eastern Caribbean region. The northern Lesser Antilles are currently affected...while Puerto Rico and the Virgin Islands are likely to be affected in the next 24 hours. Bermuda will likely be affected by Rafael on Tuesday. See Rafael special feature section below for details.

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.


This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1331Z-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.


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).

Rafael is a dynamic situation...first developing into a tropical storm in the last 36 hrs from a strong tropical wave while tracking NW across the eastern Caribbean region...and then turning north and NNE while the center regenerates under the heavy t-storms in its eastern semicircle. All the while...Rafael is quickly becoming better organized and strengthening. This discussion on this currently dynamic situation will refer to the 11 AM EDT NHC forecast (shown in Figure 1)...my 3 PM EDT forecast (also shown in Figure 1)...and the 5 PM EDT NHC forecast (not shown in Figure 1). It should be noted that the 11 AM and 5 PM EDT NHC track forecasts are quiet similar...except that the NHC has adjusted their short-term track forecast rightward to account for the reformation of the center into the heavy t-storm activity.

Track-wise...when I made my 3 PM EDT forecast shown in Figure 1...I had Rafael's center moving into the waters midway between the Lesser Antilles and Virgin Islands for late this evening as I suspected Rafael's center was regenerating into his t-storms...which made my initial track forecast have a rightward bias relative to the 11 AM NHC's. Indeed this is proving to the be the case...and the 5 PM NHC forecast has adjusted toward this solution. For the longer-term...I develop a leftward bias relative to NHC's 11 AM and 5 PM track forecasts (and even the 12Z GFS model from this afternoon) as I think these solutions underplay the amount of westward steering influence the strong 1034 mb NE US ridge (paragraph P2) is going to have as it passes north of Rafael. I agree with a rapid northward and NNE acceleration toward the end of the forecast as Rafael gets caught in the southwesterly flow ahead of the paragraph P1 weather system.

Figure 1: The 11 AM EDT NHC forecast (black line) and my 3 PM EDT forecast (red line) for Tropical Storm Rafael. I had to upgrade my intensity forecast just after 5 PM due to the strengthening that Rafael showed at 5 PM.

Intensity-wise...since inception...Rafael's east half has been under a favorable upper ridge that has been pumped-up by the system's immense t-storm latent heat release...while the west half has been suppressed by an upper trough mentioned previously in paragraph P3 of discussion #131...and now suppressed by paragraph P2 upper troughing. Because the surface center of the storm is regenerating NNE into its heavy t-storm activity...he is now strengthening a little faster than anticipated. For example in Figure 1...you can see the intensity forecast I came up with before the 5 PM update...and my newly-upped intensity forecast I came up with after the 5 PM upgrade to Rafael's strength. My upgraded intensity forecast is similar to the NHC...but my forecast strengthens Rafael into a hurricane (75+ mph) a little sooner than NHC's 5 PM forecast. This episode of strengthening is supported by the fact that models show the paragraph P2 upper troughing backing off while the favorable upper ridge/outflow over the storm grows and becomes more symmetrical. The NHC forecasts Rafael will peak at 80 mph...but I choose 75 as my left-leaning longer-term forecast track places Rafael closer to incoming southwesterly shear delivered by paragraph P1 upper trough. I also choose to keep Rafael elevated at hurricane strength late in the forecast while the NHC chooses to weaken him below hurricane force by then. My philosophy is that Rafael will maintain strength while supported by the eastern divergence of the paragraph P1 upper trough that ultimately makes him transition into a non-tropical system.

Impact swath in Figure 1 is based on the coldest-cloud tops seen in the eastern semicircle of Rafael's infrared satellite display. This swath is a larger than the tropical storm wind radius...to also account for heavy rains that Rafael's t-storm activity could deliver. Swath is extrapolated along my forecast track...and note that the swath has a rightward bias with respect to track throughout as I don't believe Rafael will ever be a perfectly symmetrical storm from current shearing of paragraph P2 upper troughing and future shearing from paragraph P1 upper trough not long after. Rafael's significant weather (particularly the heavy rains) has been slamming the Lesser Antilles for several hours...but has not yet arrived to Puerto Rico or the Virgin Islands. My more-left track forecast moreso allows the weather biased to the east side of Rafael to transfer into these currently calm areas in the next 24 hours...while the NHC forecast track would allow for the weather in Puerto Rico and Virgin Islands to be less severe. Later-on...Bermuda has a high risk of impact on Tuesday...and perhaps Newfoundland could be affected by Thursday depending on the exact track the storm takes. However...Rafael is more likely to affect Newfoundland as a vigorous non-tropical low rather than a tropical cyclone.

P1...Next upper trough and surface frontal system in the mid-latitude westerlies has entered the upper-left of the above atmo chart from the western US. Western convergence of the upper trough supports 1021 mb ridge over the 4-corners states...and eastern divergence of the upper trough supports 1002 mb frontal depression over South Dakota. Warm air advection of the 1002 mb depression has amplified an upper ridge over the central US..with directional vertical shear between the upper westerlies across the upper ridge and low-level southerlies ahead of the 1002 mb depression. The directional shear and instability from daytime heating of land has triggered severe weather and tornadoes across the central US. Visit www.nws.noaa.gov for latest central US severe weather watches and warnings with this system.

P2...Upper troughing over North America is finally shifting eastward into the W Atlantic while pushed by paragraph P1 central US upper ridge. Due to the amplitude of the central US upper ridge...the upper troughing has amplified southward into much of the Caribbean and is absorbing the central Atlantic to eastern Caribbean upper vortices mentioned in paragraph P3 of previous discussion #131. 968 mb surface gale on the east coast of Canada...once supported by the eastern divergence of the upper troughing...has weakened to 975 mb in the last 36 hrs while nearly stationary and becoming exposed to the less-divergent upper trough axis passing overhead. 1010 mb frontal depression shifting into SE Canada 36 hrs ago has intensified with the eastern divergence of the upper troughing and is now 999 mb just NE of Newfoundland. Western convergence of this upper troughing supports dry air in the W Atlantic...Gulf of Mexico...W Caribbean...and strong 1034 mb surface ridge that has shifted from the central to the NE US. 990 mb surface depression and its shortwave upper trough E of Greenland 36 hrs ago has exited the picture while moving into Europe...and yet another surface depression (less-than-996 mb) and its shortwave upper trough is heading toward Europe. This depression spun up along the occluded front of aforementioned 975 mb gale over the E coast of Canada...and the attendant shortwave upper trough is fracturing into two thanks to the strength of the central Atlantic upper ridge mentioned in paragraph P5.

P3...Upper vortex south of the Azores is retrograding SW around the central Atlantic upper ridge mentioned in paragraph P5. Convergence on the NW quad of this upper vortex supports 1027 mb central Atlantic surface ridge.

P4...Due to SW vertical shear from paragraph P2 upper troughing...Patty has dissipated as a tropical cyclone in the last 36 hours. Visible satellite this afternoon shows a series of surface swirls accelerating southwestward toward the central Bahamas while steered by strong NE US surface ridge discussed in paragraph P2. The multiplicity of swirls indicates that Patty is now a surface trough as opposed to a singular surface low. Expect dry air in paragraph P2 and the continued shear to prevent Patty from regenerating into a tropical cyclone.

P5...W Atlantic upper ridge has shifted into the central Atlantic in advance of paragraph P2 upper troughing.

P6...In the last 36 hours...a tropical wave has recently emerged from western Africa...and was placed just west of the Cape Verde Islands in TAFB maps this afternoon. Although its t-storm actvity is enhanced by divergence on the SE half of the paragraph P3 upper vortex...it is in unfavorable SW vertical shear induced by the same 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.

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3. WunderAlertBot (Admin)
9:33 PM GMT on October 14, 2012
NCHurricane2009 has created a new entry.
2. Cyclone987
1:34 PM GMT on October 14, 2012
Hello, everyone! I just signed up for the wunderground blog, and things look good already!
In my opinion, this year has been active in terms of the number of named storms, but the number of major hurricanes is well below-average for this time of year (one major hurricane - Michael). I do not like to see major hurricanes, or any tropical cyclones affecting land, I just like to see the storms that form in the open waters and intensify. Something this year is definitely prohibiting that, because we've only had one Category 4 hurricane, and by this time last year, we already had 5 Category 4 hurricanes.
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1. KoritheMan
4:51 AM GMT on October 14, 2012
I agree on Rafael becoming extratropical prior to striking Atlantic Canada. It's why I have the transition shown at day four, rather than day five like the NHC suggests.
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