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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

FXUS62 KCHS 161117

Area Forecast Discussion
National Weather Service Charleston SC
717 AM EDT Tue Jul 16 2019

The area will generally remain situated between an area of weak
inland low pressure and offshore high pressure into early next
week. Unseasonably hot and humid conditions will prevail with
fairly typical chances of showers and thunderstorms. 


As of 715 AM: The current forecast appears on track.

As of 530 AM: Based on latest high resolution guidance, I will
update the forecast to increase the mention of thunderstorms in
the forecast. Coverage appears to be the greatest over SE GA.

As of 4 AM: The center of a 594 dm H5 ridge will remain 
centered over the region today and tonight. Mild thicknesses 
under the ridge combined with strong insolation should result in
high temperatures to range from the upper 90s across the inland
areas to the mid 90s along the coast. A weak sfc trough should 
remain across the forecast area this morning, followed by a 
seabreeze this afternoon. Sfc dewpoints across the coastal 
counties should remain in the mid to upper 70s. Heat index 
values are forecast to peak between 105-109 this afternoon.

Forecast afternoon soundings indicate that a moderate subsidence 
inversion will remain just above H75. However, the hot and humid 
conditions should overcome the inversion by mid-day. During the heat 
of the afternoon, CAPE values are expected to peak around 4000 J/kg. 
Isolated to possibly scattered thunderstorms will develop along and 
west of the seabreeze this afternoon. Convection should dissipate 
within 1-2 hours following sunset. Low temperatures tonight are 
forecast to range from the mid 70s inland to the upper 70s over the 
beaches. It is noteworthy to indicate that heat index values near 
the beaches will remain in the upper 80s through tonight.


Moderate to high confidence this period. Inland troughing will 
prevail mainly north and west of the area while ridging prevails to 
the southeast. The pattern will favor a few showers near the coast 
each morning with showers and thunderstorms inland during the 
afternoon/evening. No significant risk for severe storms is expected 
due to the mostly pulse nature of the convection but certainly can't 
completely rule out isolated severe storms each day. Temperatures 
will remain above normal through the period (mainly mid-upper 90s 
inland each afternoon) with heat indices generally peaking close to 
110 degrees away from the immediate coast. Not enough confidence 
though to mention possible Heat Advisories in the Hazardous Weather 
Outlook but will need to consider this later. Overnight lows could 
also be near record high levels in the upper 70s, especially at KCHS.


Moderate confidence this period. The low-level lee-side trough looks 
to persist through the period while some upper ridging tries to give 
way to more troughing, especially by Tuesday. For now we have 
maintained a climatology and persistence forecast as far as rain 
chances (mostly around 30 percent) with temperatures remaining above 
normal. Heat indices will remain high, but mainly below the Advisory 
threshold of 110 degrees.


At 12Z, KCHS ground fog should dissipate, leaving VFR 
conditions throughout the rest of the morning. Isolated showers 
and thunderstorms will develop across the region this afternoon.
I have added a mention of VCTS for KCHS and KSAV for the 
afternoon hours. Otherwise, conditions should feature south 
winds during the daylight hours and calm to light winds at 

Extended Aviation Outlook: Low risk of flight restrictions from 
mainly afternoon/evening showers and thunderstorms through 
the weekend.


The SC/GA marine zones will remain between a inland sfc trough and 
high pressure centered over the western Atlantic. This pattern will 
result in a weak pressure gradient across the region, supporting 
southeast winds around 10 kts. Wave heights are are forecast to 
range between 1-2 ft today and tonight. Beyond 50 NM, seas may 
increase to around 3 ft late tonight.

Wednesday through Sunday: Inland low pressure and offshore high 
pressure will lead to mainly south/southwest winds through the 
period, generally highest near the coast during the afternoon from 
the sea breeze. However, conditions should stay below Small Craft 
Advisory levels as significant wave heights will be 4 feet or

Waterspouts: The environment will remain supportive for waterspout 
formation this morning. By midweek and beyond, south-southwest winds 
increase helping to lower the risk.