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2014 Atlantic Hurricane Season Birdseye Discussion #62

By: NCHurricane2009 , 3:48 AM GMT on August 13, 2014

...TUESDAY AUGUST 12 11:55 PM EDT...
Tropical wave Invest 94-L has become less organized due to dry air while moving into the waters midway between the Cape Verde Islands and Lesser Antilles. See special feature section below for an update on this tropical wave.

Two additional vigorous tropical waves are located behind Invest 94-L. The first has just moved offshore from Africa and is currently located just southeast of the Cape Verde Islands...and is not expected to develop as it will get caught in unfavorable upper-level convergence associated with the TUTT (Tropical Upper Tropospheric Trough) forecast to sag southward over the next few days (see atmospheric outlook section of the Invest 94-L special feature section for more info on the TUTT). The second tropical wave is located over interior western Africa and will emerge into the Atlantic tropical waters in about 48 hours...and has a better chance to develop below favorable low shear/good outflow associated with a tropical upper ridge to expand in the eastern tropical Atlantic in the wake of the aforementioned TUTT.

 photo Aug_12_2014_2045Z_zpsc5cacfa9.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 1932Z-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_12_2014_2045Z_Thermo_zpsb616698c.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...As of 1800Z the NHC TAFB has defined a weak 1012 mb low pressure spin centered near 13N-37W in association with the vigorous tropical wave currently located midway betwen the Lesser Antilles and Cape Verde Islands. Overall shower and thunderstorm activity has become less organized and confined to the southern part of the circulation while this system battles the dry Saharan air layer located to the north and west. In my updated forecast below I have delayed forecast tropical cyclone formation to the timeframe that is 72 hours from now as this system has become less organized in the last day.

Atmospheric Outlook for the Forecast Period...Thru the forecast period this system will be steered west around the south side of the low-level 1028 mb Atlantic subtropical ridge marked in the atmospheric features chart above...with a bend toward the west-northwest at the very end of the forecast period while arriving to the southwestern quadrant of the low-level ridge. As the chart above also shows...their is a Tropical Upper Tropospheric Trough (TUTT) north of the system marked by a series of blue dashed lines and blue Ls. This system is currently in a favorable low shear/good upper outflow environment in a tropical upper ridge south of the TUTT as marked by a blue-zig-zag line. By the middle of the forecast period...the TUTT is forecast to shift south ahead of a building upper ridge in the central Atlantic. However this system is moving fast enough to the west such that it will escape the southward-shifting TUTT and arrive beneath more favorable upper ridging to persist over the eastern Caribbean Sea. Unfavorable upper vorticity persists in the western Caribbean Sea as marked by a blue-dashed line...and this vorticity is forecast to persist thru the forecast period such that it could disrupt this system at the very end of the forecast period which is why my updated forecast below develops this system slower than previously shown.

Thermodynamic Outlook for the Forecast Period...This system is currently battling dry Saharan air located to the north and west as mentioned in the above current prognosis section. Thru the forecast period the westward track of this system will take it from waters that are currently 27 deg C to waters that are 28 to 29 deg C. The current assumption in my updated forecast below is that the increasingly warm waters will give this system enough instability to fight off the dry air such that it develops into a tropical cyclone by 72 hours.

24 Hr Forecast (0000Z August 14)...Tropical low centered near 13.5N-45W.

48 Hr Forecast (0000Z August 15)....Tropical low centered near 13.5N-53W.

72 Hr Forecast (0000Z August 16)...30 mph max sustained wind tropical depression centered near 14N-60W crossing the Lesser Antilles.

96 Hr Forecast (0000Z August 17)...35 mph max sustained wind tropical depression centered near 14.5N-67W in the eastern Caribbean Sea.

120 Hr Forecast (0000Z August 18)...40 mph max sustained wind tropical storm centered near 15.5N-72W in the central Caribbean Sea.

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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