2016 Atlantic Hurricane Season Birdseye Discussion #175

By: NCHurricane2009 , 3:16 AM GMT on November 21, 2016

...SUNDAY NOVEMBER 20 2016 10:17 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 continues to become better organized...and conditions will become more favorable for development as the base of the large upper trough over the west Atlantic and eastern North America shifts eastward and away which will allow the overhead upper ridge that is ventilating the surface low to expand. 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 1800Z and 1933Z-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 continues 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-80W and features curved thunderstorm bands around the center. This is slightly east of my previous forecast and therefore I have shifted my track forecast eastward listed below accordingly. I have also raised my intensity forecast as the eastward-adjusted track gives more time for this system to develop over water before making landfall in Central America.

Atmospheric Outlook for the Forecast Period...The surface low is currently stationary while trapped between the westerly steering flow from the upper trough and 985 mb surface frontal cyclone over the western Atlantic and eastern North America...and easterly steering flow of a strong 1032 mb surface ridge over the central North America. As the upper trough/surface frontal cyclone shift eastward and away...the unfavorable westerly vertical shear applied by the base of the upper trough 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 1032 mb ridge shifts to the north of the surface low and pushes it. By 96 to 120 hours...a pair of frontal cyclones 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 21)...35 mph maximum sustained wind tropical depression centered at 11.5N-80W

48 Hr Forecast (1800Z Nov 22)...50 mph maximum sustained wind tropical storm centered just east of southern Nicaragua at 11.5N-81.5W

72 Hr Forecast (1800Z Nov 23)...70 mph maximum sustained wind tropical storm centered just offshore of southern Nicargua at 11.5N-83W

96 Hr Forecast (1800Z Nov 24)...80 mph maximum sustained wind hurricane centered just offshore of southern Nicaragua at 11.5N-83W

120 Hr Forecast (1800Z Nov 25)...80 mph maximum sustained wind hurricane centered just offshore of southern Nicaragua at 11.5N-83W


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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