2014 Atlantic Hurricane Season Birdseye Discussion #79

By: NCHurricane2009 , 6:20 AM GMT on August 31, 2014

...SUNDAY AUGUST 31 2014 2:30 AM EDT...
Tropical wave Invest 99-L remains at risk for additional development while moving across the Yucatan and into the Bay of Campeche over the next 48 hours. See special feature section below for additional details.

The eastern Atlantic tropical wave from Africa that was a special feature in discussions #75 and #76...and a tropical wave in the central tropical Atlantic...are contributing to an elongated 1012 mb low pressure system that apperas to be becoming well organized and consolidating near 10N-38W. I have upgraded this system to a special feature on this blog. See second special feature section below for additional details. Interests in the Lesser Antilles should monitor the progress of this system over the next few days.

Shower and thunderstorm activity of a tropical wave over western Africa has rapidly increased between 1200Z and 1800Z this past afternoon. Waiting to see if this activity persists with this tropical wave before upgrading it to a special feature on this blog.

 photo Aug_30_2014_2245Z_zps4e743531.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 1926Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

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 Aug_30_2014_2045Z_Thermo_zpsf9cd2845.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).

Current Prognosis...Even though the shower and thunderstorm activity associated with this tropical wave is less concentrated relative to 24 hours ago...a spin appears to be developing along the wave axis and was located at 18N-86W as of 0000Z.

Atmospheric Outlook for the Forecast Period...This system will be in a favorable low shear environment on the south side of Gulf upper ridging during the forecast period (marked by blue-zig-zag line and blue H north of 99-L in the above atmospheric features chart). Because this system will be south of the upper ridge axis...if it does develop it will show limited upper outflow on its north side but plenty of equatorward outflow. Track is expected to be west-northwest curving to the northwest at the very end of the forecast period on the southwest side of subtropical low-level ridging...with the system not expected to curve north while missing the ridge weakenesses associated with the current east-central US upper trough/1006 mb frontal cyclone and western US upper trough/1004 mb frontal cyclone following behind.

Thermodynamic Outlook for the Forecast Period...As the thermodynamics chart above shows...this system will be embedded in a very favorable thermodynamic environment thru the forecast period while tracking over 31 to 32 deg C waters and thru a moist airmass.

24 Hr Forecast (0000Z September 1)...Tropical wave axis producing an organizing tropical low over the southern Yucatan Peninslula near 18.5N-90W.

48 Hr Forecast (0000Z September 2)...Organized tropical low over the central Bay of Campeche centered near 19.5N-94.5W

72 Hr Forecast (0000Z September 3)...40 mph max sustained wind tropical storm centered near 20.5N-98W inland over east-central Mexico

96 Hr Forecast (0000Z September 4)...Remnant low over east-central Mexico centered near 22.5N-99W

Current Prognosis...A well organized tropical low is located at 10N-38W as of 0000Z and is taking advantage of low shear/enhanced outflow below tropical upper ridging (marked by a blue-zig-zag line in the lower right of the above atmospheric features chart). Satellite animation between 1800Z and 0000Z suggests that this tropical low has moved from 35w to 38W...or at a rate of about 3W in 6 hours which is approximately 10 to 12W in 24 hours upon which the early portion of the forecast track below is based on.

Atmospheric Outlook for the Forecast Period...The 1028 mb Atlatnic subtropical ridge which is pushing this system westward is expected to weaken thru the forecast period as the southern portion of the upper trough associated with non-tropical Cristobal merges with what is now a northern fracture of the central US upper trough which is currently over eastern Canada...with the merged cut-off upper trough supporting an impressive surface low that weakens the ridge and obliterates the eastern part of the ridge. The weakening of the ridge will cause the westward speed of the track to slow as this system enters the Caribbean as reflected in the forecast track below. The forecast below also suggests the track bending more northward as this system is predicted to be strong/tall enough to be tugged by the east side of what is now the upper vortex near the Bahamas marked by a blue L/blue-dashed line in the above atmo chart (this upper vortex is expected to last and be generally stationary thru the forecat period). In addition...this upper vortex is likely to impart some westerly shear on this system at the end of the forecast period which is why the forecast intensification rate is flattened during that time.

Thermodynamic Outlook for the Forecast Period...This system is currently over favorable 28 deg C...and will track toward even more favorable waters of 29 to 30 deg C by the end of the forecast period. The above thermo chart shows that the dry Saharan air layer is weaker than ever before during this hurricane season...which is also a favorable factor for this system.

24 Hr Forecast (0000Z September 1)...Organized tropical low centered near 10N-48W

48 Hr Forecast (0000Z September 2)...40 mph max sustained wind tropical storm centered near 11N-58W approaching the southern Lesser Antilles

72 Hr Forecast (0000Z September 3)...60 mph max sustained wind tropical storm centered near 12N-65.5W in the eastern Caribbean Sea

96 Hr Forecast (0000Z September 4)...70 mph max sustained wind tropical storm centered near 14.5N-70.5W in the central Caribbean Sea under light westerly shear

120 Hr Forecast (0000Z September 5)...75 mph max sustained wind hurricane centered near 17N-75.5W just southeast of Jamaica

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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