2014 Atlantic Hurricane Season Birdseye Discussion #17

By: NCHurricane2009 , 3:41 AM GMT on June 19, 2014

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...WEDNESDAY JUNE 18 2014 11:45 PM EDT...
Shower and thunderstorm flare ups still continue in the southern Caribbean Sea as a surface tropical wave interacts with upper divergence ahead of a cut-off upper vortex that has retrograded from Cuba and the Bahamas and into the southeastern Gulf of Mexico. The persistence of this activity appears to have re-built an upper ridge due to the latent heat release of the thunderstorms. With the retrograding of the upper vortex and reformation of an upper ridge...upper winds have trended more favorably for tropical development and therefore I have re-introduced this system as a special feature on this blog. See special feature section below for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jun_18_2014_2045Z_zps492f50a8.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1916Z-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.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jun_18_2014_2045Z_Thermo_zpsc2efa4f8.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).

...SPECIAL FEATURE...SOUTHERN CARIBBEAN DISTURBANCE...
Current prognosis...As stated in the intro of the previous and current discussion...disturbed weather currently located just east of Nicaragua and Honduaras in the southern Caribbean is being driven by surface convergence of a tropical wave currently moving into Central America interacting with upper divergence around the rim of a cut-off upper vortex. In the above atmo chart...the tropical wave is marked by a red-dashed line and "TW" notation...and the upper vortex is marked by a blue L just due north of the tropical wave. The persistence of the thunderstorms appears to have generated a Caribbean upper ridge via latent heat release as marked by a blue-zig-zag line located just east of the tropical wave. The formation and expansion of this upper ridge maybe partly why the upper vortex has been pushed to a westward retrograding motion from Cuba/Bahamas and into the SE Gulf of Mexico over the last 24 hours.

Atmospheric Outlook for the Forecast Period...Current assumption is that southeastern Gulf of Mexico upper vortex will weaken while becoming squeezed between expanding Caribbean upper ridge (supported by latent heat release of the disturbance's thunderstorms) and upper ridge ovr the eastern United States (supported by hot air mass propped up by warm air advection ahead of frontal systems). As the upper vortex weakens while the Caribbean upper ridge expands over the disturbance...this will reduce the current unfavorable levels of wind shear.

Thermodynamic Outlook for the Forecast Period...Sea surface temps across the Caribbean are in the 27 to 29 deg C range...favorble for tropical cyclone development. Current assumption is Caribbean upper ridge will be sustained or be expanding thru the forecast period...which will support upper divergence and hence rising motion over the area that will keep the environment moist.

24 Hr Forecast (1800Z June 19)...Tropical wave to leave behind area of disturbed weather while crossing Central America. Currently predicting thunderstorms to persist in the southern Caribbean in upper divergence southeast of cut-off upper vortex and west of Caribbean upper ridging. Also currently forecasting the formation of a small surface tropical low in the thunderstorms just east of Nicaragua in the vicinity of 83W-14N.

48 Hr Forecast (1800Z June 20)...Same dynamics as 24 Hr forecast...with surface low predicted to become better organzied in the vicinity of 83W-14N.

72 Hr Forecast (1800Z June 21)...Forecast tropical cyclone formation just east of Nicaragua in the vicnity of 83W-14N.

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