2016 Atlantic Hurricane Season Birdseye Discussion #174

By: NCHurricane2009 , 10:10 PM GMT on November 19, 2016

...SATURDAY NOVEMBER 19 2016 5:11 PM EDT...
The following statement concerns area of interest #1 marked in the central Caribbean Sea in the atmospheric features chart below. The area of disturbed weather in the region supported by a surface low has already become better organized...and conditions will become more favorable for development as the bases of both the upper troughs in the west Atlantic and eastern North America shift eastward and away which will allow the overhead upper ridge that is ventilating the surface low to expand. Therefore I have upgraded this system to a special feature on this blog with a tropical cyclone formation forecast...see the special feature section below for additional details on this developing situation. Interests in Nicaragua and Costa Rica should monitor the progress of this disturbance as it could develop into a strong tropical storm or possibly a hurricane while slowly moving toward Central America over the next few days.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z and 1329Z-released WPC analysis.

Areas of Interest maybe first introduced circled by a yellow-dashed line. If the area of interest becomes introduced in the 5-day National Hurricane Center (NHC) Atlantic tropical weather outlook then it gets upgraded with a green-dashed line encircling it. If the area of interest gets upgraded to an Invest or is mentioned in the 48-hour NHC Atlantic tropical weather outlook then it gets upgraded with a green-solid polygon encircling it.

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 (also called an upper vortex or upper cyclone), blue Hs are locations of upper ridges (also called upper anticyclones).

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. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows (cyclones), Hs indicate surface highs (ridges/anticyclones).

...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...CARIBBEAN SURFACE LOW INVEST 90-L...
This special feature section is for area of interest #1 marked in the above atmospheric features chart.

Current Prognosis...The surface low that has persisted in the south-central Caribbean Sea over the last few days has finally begun to become better organized while aided by warm sea surface temperatures and upper-level outflow from an overhead upper ridge. As of 1800Z earlier this afternoon the center of the surface low was pinwheeling stationary at 11.5N-81W and features curved thunderstorm bands around the center.

Atmospheric Outlook for the Forecast Period...The surface low is currently stationary while trapped between the westerly steering flow from the upper troughs and 990 mb and 992 mb surface frontal cyclones over the western Atlantic and eastern North America...and easterly steering flow of a strong 1040 mb surface ridge over the central United States. As the pair of upper troughs/surface frontal cyclones shift eastward and away...the unfavorable westerly vertical shear applied by the bases of both upper troughs will reduce and the favorable overhead upper ridge will expand. In addition the surface low will likely begin moving westward toward Nicaragua and Costa Rica while the 1040 mb ridge shifts to the north of the surface low and pushes it. By the end of the 120-hour forecast period...another frontal cyclone moving into eastern North America will weaken the ridge which could cause the surface low to stall again.

Thermodynamic Outlook for the Forecast Period...The surface low will be over favorable 29 deg C waters in the southern Caribbean supportive of tropical development.

24 Hr Forecast (1800Z Nov 20)...Surface low centered at 11.5N-81W

48 Hr Forecast (1800Z Nov 21)...35 mph maximum sustained wind tropical depression centered at 11.5N-81W

72 Hr Forecast (1800Z Nov 22)...50 mph maximum sustained wind tropical storm centered just east of southern Nicaragua at 11.5N-82.5W

96 Hr Forecast (1800Z Nov 23)...70 mph maximum sustained wind tropical storm centered over southeastern Nicaragua at 11.5N-84W

120 Hr Forecast (1800Z Nov 24)...35 mph maximum sustained wind tropical depression centered over southeastern Nicaragua at 11.5N-84W


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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