2013 Atlantic Hurricane Season Birdseye Discussion #19

By: NCHurricane2009 , 6:12 AM GMT on June 19, 2013

...WEDNESDAY JUNE 19 2013 2:10 AM EDT...
Tropical depression two has moved across Belize...northern Guatemala...southeastern Mexico...and into the Bay of Campeche on a more northerly than expected trajectory. As a result...it will now track moreso over the warm open waters of the Bay of Campeche and has what I now forecast a high risk of becoming a tropical storm before making landfall in east-central Mexico on Thursday morning. Visit www.nhc.noaa.gov for latest info on this tropical cyclone and associated tropical storm advisories currently in effect for east-central Mexico. See special feature section below for additional details on tropical depression two.

As promised in my final 2012 hurricane season birdseye discussion...I have begun to release post-storm reports for the 2012 Atlantic Hurricane Season which includes evaluations of how my storm forecasts (issued on these birdseye discussions) compared with that of the official forecasts from the National Hurricane Center. As these post-storm reports come out...they can be viewed on my other blog thread at www.wunderground.com/blog/MIHurricane2009.

 photo Jun_18_2013_2345Z_zps31e8056e.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0129Z-released WPC 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.

 photo Jun_18_2013_2345Z_zps8052d00e.png
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).

As mentioned in the intro statement of this discussion and as shown by the NHC recorded storm track in Figure 1...tropical depression two has tracked more northward than expected...and as a result its center has just recently entered the Bay of Campeche. During my previous special feature section on tropical depression two...it was assessed the depression was under some southerly shear west of the paragraph P6 Caribbean upper ridge center and east of the paragraph P5 upper vortex. Perhaps with the thunderstorms being biased a bit to the north side under the shear...maybe we saw a northward regeneration of the circulation below those thunderstorms. Or perhaps the east side of the paragraph P5 upper vortex was low enough in the atmosphere to impart a northward drag on this shallow tropical depression's track. If its to be believed the northward motion was caused by center reformation below thunderstorms...it now appears the center is basically collocated with a small t-storm cluster over open water such that no more northward motion should occur. If its to be believed the northward motion was cuased by the east side of the paragraph P5 upper vortex...the depression is now north of the upper vortex such that no more northward motion should occur.

With it assessed that the forces pulling the depression more northward coming to a close...in the next 12 hrs I gradually expect it to return to the WNW track it had at birth...a track parallel to the isobars of the west extension of the paragraph P4 low-level ridge and 1021 mb Great Lakes/Hudson Bay ridge mentioned in paragraph P1. As mentioned in my previous discussion of tropical depression two...computer model runs such as GFS insist on building a blocking low-level ridge over Mexico and due west of the tropical depression. By again studying the GFS models today...I now believe this low-level ridge will form in the next 24 hours due to upper-level convergence at the SW end of the paragraph P1 central US upper trough...due to upper-level convergence west of the forecast SE US shortwave upper trough mentioned in paragraph P7...and due to upper-level convergence east of an upper ridge ahead of the next mid-lat upper trough about to enter the above charts (this upper convergence may be enhanced if the strengthening of TD 2 results in a strong upper anticyclone over TD 2 that clashes with that upper ridge). However unlike the GFS...I don't think the forecast Mexico low-level ridge will be due west of the system as to slow/stall its forward speed...but rather due northwest of the depression such that it tracks straight west with its current speed after 24 hrs. Basically my forecast track in Figure 1 below agrees with the NHC expect that I show a bit of a northward bias to account for the fact that the most recent segment of the NHC recorded storm track has not yet shown a bend back to a WNW track.

Even though the depression is under some southerly shear west of the paragraph P6 upper ridge and east of the paragraph P5 upper vortex...the upper winds directly over the depression are anticyclonic and divergent such that the southerly shear is not strong and such that upper winds are rather favorable for development over the warm 30 deg C Bay of Campeche waters. In fact by looking at the very latest satellite-derived upper wind barbs...it seems like TD 2 could soon develop its own mini-anticyclone above itself and within the larger-scale paragraph P6 upper ridge...which would reduce the shear even further (even if this is not the case...paragraph P7 explains that the core of the upper ridge is headed westward toward TD 2 which will also reduce the shear further). With very warm waters...favorable upper winds...and a t-storm burst near the center...I am making my intensity forecast higher than the 10 PM CDT NHC forecast...predicting intensification to a 45 mph max wind tropical storm by tonight.

 photo Jun_18_2013_TD_2_Forecast_zpsa3ab3bd2.png
Figure 1: Forecast for Tropical Depression Two

Current colorized infrared satellite shows t-storm burst near the center and a mass of t-storms to the southeast...so I intialized my impact swath in Figure 1 based on that structure. I predict that as TD 2 strengthens and consolidates over the Bay of Campeche...the central t-storm burst will grow in size whereas the t-storm mass southeast of center gets pulled into the central t-storm burst...and so the evolution of my impact swath is based on this prediction while moving the system along my forecast track. Impact statement (b) is added due to the propsect of this system strengthening into a tropical storm.

P1...Upper trough originating from western Canada is now a major feature across the central US extending into eastern Canada. Within the last 12 hours...eastern divergence of this upper trough has supported surface frontal cyclogenesis over the Ohio/Tennesse Valleys...and since then the frontal cyclone has tracked eastward where it now has a 1009 mb center over North Carolina. Western convergence of this upper trough supports 1021 mb surface ridge near Hudson Bay and the Great Lakes that is building rapidly behind the 1009 mb center. To the southeast of the upper trough...former United States upper ridge is reduced to a Florida/W Atlantic upper ridge supported by low-level warm air advection ahead of the 1009 mb center. Meanwhile...a fragment of this upper trough dove past the upper ridge 6 days ago...where we now have an upper trough that has moved from the west Atlantic into the north-central Atlantic with attendant less-than-984 mb frontal cyclone currently located SE of Greenland that is supported by the eastern divergnce of this north-central Atlantic upper trough. Meanwhile western convergence if this north-central Atlantic upper trough supports new 1015 mb surface ridge just offshore of the east Canada coast.

P2...Relatively new upper vortex N of the Cape Verde Islands...mentioned in paragraph P2 of the previous discussion....persists in relatively lower pressures between upper anticyclone mentioned in paragraph P4 and eastern Atlantic low-latitude upper ridge mentioned in paragraph P8.

P3...Cut-off upper vortex persists in the open central Atlantic.

P4...Surface ridge dominates much of the open Atlantic basin. Its main center...currently 1034 mb...is now stacked with upper anticyclone near the Azores...effectively creating a deep-layered anitcyclone over the Azores at the moment. This upper anticyclone is a result of warm air advection ahead of the less-than-984 mb frontal cyclone mentioned in paragraph P1 above. This surface ridge has had a westward extension into the Gulf of Mexico over the past days due to what is now southeastern convergence of what is now the Florida/W Atlantic upper ridge mentioned in paragraph P1.

P5...Cut-off Upper trough over SE Mexico and the Bay of Campeche in the previous discussion has continued to be pushed westward thanks to the warming provided by tropical depression two's t-storm latent heat release. As a result of its continued westward track...this upper trough has now moved out of the scope of the above charts and into the eastern Pacific as an upper vortex.

P6...Western half of the Caribbean Sea continues to be dominated by upper-level anticyclonic ridge in part associated with the outflow structure of Tropical Depression Two.

P7...Tropical wave crossing the southern Lesser Antilles mentioned in paragraph P6 of the previous discussion is now over NW Venezuela. Cut-off upper vortex left south of Bermuda by what is now the paragraph P1 north-central Atlantic upper trough (mentioned in paragraphs P1 and P6 of previous discussion #18) is suppressing activity associated with this tropical wave...but is simultaneously enhancing thunderstorms over the Lesser Antilles with divergence at its southeastern quadrant. In the next 48 hrs...a shortwave upper trough will eject into the SE US (originating from next mid-lat upper trough not yet in the scope of the above charts)...with a new Florida upper ridge forming in relatively higher pressures between the SE US shortwave and upper vortex south of Bermuda. In turn...a fragment of that upper vortex will retrograde SW around the Florida upper ridge...which in turn will push the paragraph P6 upper ridge westward.

P8...Low-latitude upper ridge remains in the eastern tropical Atlantic. Although a tropical wave that has recently rolled off of Africa is currently SSW of the Cape Verde Islands and below this favorable upper ridge...the eastern tropical Atlatnic remains quiet under a recent westward expansion of dry air seen in the lower-right of the above thermo chart. It appears this expansion of dry air is a plume of Sahara Desert air advected westward by the deep-layered Azores anticyclone mentioned in paragraph P4.

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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