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By: NCHurricane2009 , 12:01 AM GMT on August 08, 2012
...AUGUST 7 2012...8:01 PM EDT...
This discussion has been released 17 hours after the following graphics were created. This is due to another attempt at experimental 200-mb and surface outlook graphics that are time-consumptive for me to generate. Therefore...I have decided this is the last time I will attempt these outlooks.
Ernesto becomes a hurricane this afternoon...set to make landfall across Mexico's Yucatan peninsula beginning tonight. Later this week...Ernesto is expected to cross the Bay of Campeche waters and make a second and final landfall into mainland Mexico. Meanwhile...Florence's remnant low is at a higher risk of regenerating than previously thought..and yet another tropical wave (recently classified as Invest 92-L) is at risk of tropical cyclone formation. See all three special feature sections for further details on Ernesto...Florence...and Invest 92-L.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0121Z-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.
5-day surface outlook created at 1800Z yesterday. The streamlines represent lower-level atmospheric flow...ONLY drawn at the well-defined perimeter of surface ridge flows. Cyclonic flow is assumed to be occurring between the surface ridge flows. 0-hour flow is based on initialization of GFS computer model surface to 10-meter depth (shown on NOAA's MAG page). Flow beyond 0-hour is based on GFS model wind barb display for its surface to 10-meter high forecast (also shown on NOAA'S MAG page).
5-day 200-mb (upper-level) outlook created at 1200Z. The streamlines represent upper-level atmospheric flow...ONLY drawn at the well-defined perimeter of upper-level trough/vortex flows. Anticyclonic flow is assumed to be occuring between the upper-level trough/vortex flows. 0-hour flow is based on 200-mb wind barbs in above atmospheric birdseye chart. Flow beyond that is based on GFS model wind barb display for its 200 mb forecast...shown on NOAA's MAG page.
...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 ERNESTO...
Since previous discussion #72 (4:30 AM EDT Aug 6)...Ernesto was battling inverted upper trough aloft and dry air to his west. Yesterday (Aug 6) afternoon...Ernesto's thunderstorm latent heat release defeated the inverted upper trough earlier than I expected...and he quickly strengthened to 65 mph winds. Last evening (Aug 6)...Ernesto consumed the remainder of the dry air to his west...which halted intensification beyond 65 mph winds. Due to the dry air ingestion...my forecast graphic in Figure 1 below (generated early this morning) barely had Ernesto become a 75 mph max wind hurricane before making landfall in the Yucatan. Otherwise the rest of the intensity forecast in Figure 1 below is a copy-paste of my previous intensity forecast from discussion #72.
Predicting exactly when the dry air would mix out is difficult...but he has done so ahead of schedule and quickly become an 80 mph max wind hurricane this afternoon. So the only intensity forecast correction I am going to make now is to say that the 11 PM Tue point in Figure 1 (representing tonight's landfall in Yucatan) should be upped from 75 to 80 mph max winds. Ernesto is running out of time for additonal strengthening as his center is near the Yucatan shore as of this writing.
Figure 1: Tropical Storm (now Hurricane) Ernesto forecast graphic created early this morning.
Low-level steering solution (using above 5-day surface outlook).......Current ex-91L/paragraph P1 cold front surface ridge weakness shows as an inverted E Gulf of Mexico trough wedged between central US ridge (paragraph P1) and Atlantic ridge (paragraph P5). This inverted trough is shown collapsing thru 48 hr (11 PM Wed) as Atlantic ridge rebuilds in. Due to second impulse in paragraph P1...ridge weakness re-establishes itself across eastern US starting at 72 hr (11 PM Thu)...the weakness growing into the N Gulf of Mexico thru 96 and 120 hrs (11 PM Fri and 11 PM Sat). In conclusion...from surface perpsective...dissipation of E Gulf inverted trough suggests steady WNW steering thru 48 hrs (11 PM Wed)...weakening in WNW steering by 72 hrs (11 PM Thu)...then collapse in steering in 96 and 120 hrs (11 PM Fri and 11 PM Sat).
Upper-level steering soliuton (using above 5-day 200 mb outlook).......Paragraph P4 upper vortex is being pushed away from Ernesto by its vigorous upper anticyclonic outflow. Therefore...I keep this upper vortex a non-factor in Ernesto's upper-level steering solution. This leaves SW US upper ridge (paragraph P1) and upper trough (also in paragraph P1). The paragraph P1 upper trough amplifies southward and erodes SW US upper ridge thru 48 hrs (almost to suggest gradual collapse in upper steering solution thru 48 hrs...which is 11 PM Wed based on outlook's released time). The 200 mb 5-day outlook hints the SW US upper ridge recovers and noses in from the west after 48 hrs (after 11 PM Wed)...which would help in a westward upper-level steering solution by that time and onwards.
In Figure 1...my track forecast still has a northward bias compared to NHC's...because of Ernesto's tendency to be tracking more north than expected over last several hours...but also due to how I blend the above upper-level and surface steering solutions. Since the above upper-level steering solution is collapsed thru 11 PM Wed...I will be using the first 48 hrs worth of above lower-level steering solution regardless of how strong Ernesto gets...which is a steady WNW push. Between 11 PM Wed and 11 PM Thursday...I slow down Ernesto (behind NHC's suggested speed) as the above low-level steering solution starts weakening. There is also a westward bend in track beginning 11 PM Thu and onwards...as I believe Ernesto will be re-strengthening over Bay of Campeche waters...allowing him to feel more of the above upper-level steering solution. With 96 and 120 hr (11 PM Fri and 11 PM Sat) low-level steering solution collapsed...by that time I am depending fully on Ernesto's ability to continue strengthening and feeling the upper-level steering solution...which would take him westward into mainland east-central Mexico by Friday/Saturday. Not sure about NHC's forecasted WSW bend by Friday/Saturday...unless the SW US upper ridge will be strong enough to give a southward component to his track by that time.
...SPECIAL FEATURE...REMNANT LOW OF FLORENCE...
Florence's remnant low has moved directly under paragraph P6 upper ridge axis for better upper outflow...and combined with warmer water temps...she has begun re-flaring t-storms over her center. Despite the presence of dry air...these current dynamics are why I initially had kept Florence strong in my first forecasts during discussions #71 and #71A.
The dry air that caused Florence to weaken into a remnant low in the first place (source of dry air in paragraph P5) is still plentiful...keeping the new t-storm flares only intermittent. The next obstacle noted for Florence's remnant in previous discussion #72 is southwesterly vertical shear due to mid-ocean upper vorticity (paragraph P3). Above 200-mb outlook suggests the SW shear is parked stationary thru 24 hrs (which is 11 PM tonight due to the release time of above graphic). This stationary shear is located at 50W longitude and westward...and Florence is currently nearing that longitude. However...prospects for Florence to regenerate into a tropiacal cyclone are increasing...as above 200-mb outlook is aggressive in weakening the mid-oceanic upper vorticity. When comparing the above 96 hr 200-mb outlook to the discussion #72 120 hr 200-mb outlook...the weakening forecast for this upper vorticity is more aggressive than ever...which would reduce the SW shear and increase chances for Florence to regenerate. On the other hand...if the above 200-mb outlook does not pan out (i.e. the upper vorticity does not weaken as fast)...then Florence will fail to regenerate due to southwesterly shear.
Track-wise...so far Florence has been closely following my forecasted straight west track shown in Figure 2 of the previous discussion...as her shallow structure is steered westward by paragraph P5 surface ridge. Albeit...she looks like she has re-gained some vertical depth and appears to be bending more north in track...gravitated toward paragraph P3 upper vorticity. As a rule of thumb...the stronger Florence becomes...the more north she will track due to the paragraph P3 upper vorticity. The longer she stays weaker...the more west she will track due to paragraph P5 surface ridge.
...SPECIAL FEATURE...TROPICAL WAVE INVEST 92-L...
A tropical wave in the eastern tropical Atlantic has been continuously organizing since it left Africa...and is currently located WSW of the Cape Verde Islands and east of Florence's remnant low. Its t-storm driven latent heat release has been trying to locally flare up the paragraph P6 upper ridge and establish an upper outflow structure. Because most of this latent heat release has occurred on the south side of the upper ridge...this has increased the speed of upper eastelry winds...hence increasing the easterly vertical shear.
Its thunderstorms...supported by whatever upper outflow structure it has now...have been sufficient in keeping out paragraph P5 dry air. Due to SW-NE orientation of paragraph P6 upper ridge in this part of the Atlantic...with time the continued west track of the tropical wave will take it more directly beneath the upper ridge axis for less shear/more symmetrical upper outflow...similar to what is now occurring with Florence's remnant low. With this reasoning...I expect this tropical wave to become a tropical cyclone in the next days. It will track more WNW toward paragraph P3 upper vorticity the sooner it develops into a stronger/vertically deeper tropical cyclone. Atlernatively...if no development occurs...it will continue straight west under the guidance of the Atlantic (paragraph P5) surface ridge.
P1...Upper trough over central US and central Canada persists....with the frontal cyclone it supports swinging east across E Canada and into the Atlantic high seas SW of Greenland while intensifying to 989 mb. A second impulse...another frontal cyclone from W Canada...has swung into Hudson Bay with a 1002 mb center...its cool air advection re-enforcing this upper trough. Central US surface ridge has weakened from 1025 to 1018 mb due to incoming 1002 mb cyclone...but this surface ridge should re-position/re-build behind this surface cyclone with support of upper convergence on back side of the upper trough. Low-level warm air advection ahead of 989 mb cyclone supports W Atlantic upper ridge...while SW US upper ridge persists behind this upper trough.
P2...Longwave upper trough regime continues across Atlantic high seas. Deep-layered low has pushed into west Europe...but its upper trough lingers behind in NE Atlantic. Frontal depression S of Greenland is diving SE toward the Azores....as its supporting shortwave upper trough swings SE and merges with NE Atlantic upper trough.
P3...Mid-ocean upper vorticity persists....now featuring a few upper vortex centers. In past 36 hrs...shortwave upper trough S of Greenland (paragraph P2 above) contributed to and re-enforced this upper vorticity.
P4...Cut-off upper vorticity in Gulf of Mexico is retrograding westward toward S Texas and Mexico....pushed vigorously by the strong upper anticyclonic outflow of Hurricane Ernesto.
P5...Atlantic surface ridge of 1023 to 1025 mb centers is supported by a few upper convergent sources while stretching from Gulf of Mexico to waters offshore of W Europe....including convergence SE of the of west Atlantic upper ridge (paragraphs P1)...and convergence behind NE Atlantic upper trough (paragraph P2). South side of this surface ridge is helping to waft Africa desert dry air westward across the Atlantic tropics. However...this dry air is reduced due to moisture from Hurricane Ernesto and tropical wave Invest 92-L. Within this surface ridge...surface trough was recently supported by upper divergence between mid-ocean upper vortex in paragraph P3 and W Atlantic upper ridge (paragraphs P1). Now...this surface trough is supported by split flow divergence between two of the upper vortices in paragraph P3. This surface trough has recently been steered SW by this surface ridge and toward the waters E of the Bahamas. Decaying front extending from W Europe deep-layered cyclone (paragraph P2) also cuts into this surface ridge...with a 1020 mb low near the Azores...and 1016 mb low in south Spain.
...TROPICAL BELT DISCUSSION...
P6...Upper ridge continues to cover all of the Atlantic tropics. T-storm latent heat release from Hurricane Ernesto...occasionally from the remnants of Florence...and tropical wave Invest 92-L...continue to locally inflated this upper ridge into cells of upper anticyclonic outflow...with upper troughs forming between these cells. The upper trough E of the Lesser Antilles has finally merged with the mid-ocean upper vorticity mentioned in paragraph P3. Inverted upper trough between Florence's anticyclone and Invest 92-L's developing upper anticyclone persists...now located midway between the Lesser Antilles and Cape Verde Islands. Based on how low-amplitude this inverted upper trough has been...now I think it has too much representation in the above 200-mb outlook...which shows this inverted upper trough gradually going into the SE Caribbean over the next 5-days.
P7...Tropical wave fragment (surface trough) over north Florida...formerly tropical disturbance Invest 91-L...has dissipated several hours ago.
P8...Tropical wave approaching Lesser Antilles in previous discussion has crossed those islands into the eastern Caribbean Sea. Westerly vertical shear from paragraph P3 upper vorticity is preventing any tropical development here.
P9...Based on satellite imagery...next tropical wave from Africa has been continuously organzing into a low pressure spin while passing south of the Cape Verde Islands. It has been upgraded to tropical disturbance Invest 92-L. Hence this tropical wave has received its own special feature section above. See that special feature section for additional details on this situation.
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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