textproduct: Charleston

WHAT HAS CHANGED

Extreme Heat Warnings and Heat Advisories have been issued for dangerous heat on Tuesday.

KEY MESSAGES

- 1) Heat will remain a concern through the middle of the week.

- 2) Some strong to severe thunderstorms are possible each afternoon this week.

DISCUSSION

KEY MESSAGE 1: Heat will remain a concern through the middle of the week.

This Afternoon and Evening: Hot and oppressive conditions will continue this afternoon and gradually come to an end early this evening. Visible satellite shows the effects of the expansive ridge and dry air aloft. Bubbling cumulus over extreme southeastern SC and southeastern GA converging with the struggling sea breeze is the only hint a the potential for a stray shower or thunderstorm late this afternoon. Heat headlines remain in effect for the entire through this evening.

Tuesday: Hot/humid conditions will remain across the Southeast United States with large-scale ridging centered across the Deep South and northern Gulf regions. Record warmth is possible, especially as the heat wave peaks with another day of favorable downslope flow across the local area. Many areas could see temps peak around 100 degrees along the I-95 corridor as afternoon convection is limited. The setup favors some mixing out of sfc dewpts across inland areas, but moisture pooling along/near an afternoon sea breeze supports sfc dewpts in the mid-upper 70s. An Extreme Heat Warning has been issued for areas along and east of I- 95. Latest probabilistic guidance supports slightly higher dew points on Tuesday, therefore the Extreme Heat Warning has been expanded a row of counties inland across the SC Lowcountry and southeastern GA.

Wednesday into Friday: There are signs of the expansive ridge starting to weaken while scattered convection returns during peak heating hours mid to late week. We could see Heat Advisory conditions prior to showers/thunderstorms developing Wednesday and Thursday, especially along the coastal corridor. Friday remains warm, but guidance supports greater convective coverage and some relief from the heat during peak heating hours, as shortwave energy associated with a large-scale trough approaches the Mid-Atlantic and Southeast states this weekend.

KEY MESSAGE 2: Some strong to severe thunderstorms are possible each afternoon this week.

The heat and humidity mentioned in Key Message 1 will provide instability across our area each afternoon this week. While each model has differences regarding how much will be in place and where the highest values will be, the general consensus seems to be SBCAPE values in the 2,000-3,000 J/kg range with locally higher peaks. DCAPE values should easily exceed 1,000 J/kg. There are notable differences between the various CAMS and the deterministic models, with many pointing to it being dry each afternoon or minimal convection. However, the amount of instability in place is hard to ignore. Likewise, it won't take much for isolated to scattered convection to form along the sea breeze each afternoon and then shift inland. Therefore, we raised POPs each afternoon, generally going with slight chance to chance. The outflow and boundary interactions should play a major role in additional storm formation and persistence. Strong to severe thunderstorms are possible each afternoon with the main threat being damaging winds. Heavy rainfall is also a concern due to the very weak steering winds and elevated PWATs. Backbuilding and/or training of storms could drop enough rainfall to generate very localized flooding. Any convection should dissipate each evening with the setting sun.

AVIATION /18Z MONDAY THROUGH SATURDAY/

18Z TAFs: VFR. An isolated shower or storm is possible along the sea breeze this afternoon, but chances of direct impact to TAF sites is low. Winds remain elevated tonight, therefore stratus and fog chances are low.

Extended Aviation Outlook: VFR conditions expected at all terminals Tuesday through Thursday, although limited impacts are possible with isolated showers and thunderstorms during afternoon hours. Chances for afternoon shower/thunderstorms increase this weekend, which could result in TEMPO flight restrictions at all terminals.

MARINE

Tonight and Tuesday: Winds remain elevated overnight, gusting up to 20 knots at times. Typical summertime winds continue into Tuesday. Similar conditions are expected on Tuesday afternoon with the strongest winds near the sea breeze. Seas will average 2-3 ft within 20 nm and 3-4 ft in the 20-60 nm leg.

Extended Marine: There will be areas of high pressure in the western Atlantic and the northern Gulf, while surface troughing persists over the Southeast United States. The interaction between these synoptic features will support a typical summertime wind pattern with winds/seas that remain below Small Craft Advisory levels. In general, southwest winds should back to a more south direction each day, peaking in speed along the coast due to a sea breeze, then return to southwest during the overnight period. Seas will mainly be in the 2-3 ft range.

CHS WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory until 8 PM EDT this evening for GAZ087-088- 099>101-114-115-137-216-218-238. Heat Advisory from 11 AM to 8 PM EDT Tuesday for GAZ087-088- 099-100-114-115-137. Extreme Heat Warning from 11 AM to 8 PM EDT Tuesday for GAZ101- 216>219-238>241. Extreme Heat Warning until 8 PM EDT this evening for GAZ217- 219-239>241. SC...Heat Advisory until 8 PM EDT this evening for SCZ040-042>044- 147. Heat Advisory from 11 AM to 8 PM EDT Tuesday for SCZ040-042- 043. Extreme Heat Warning from 11 AM to 8 PM EDT Tuesday for SCZ044- 045-147>152. Extreme Heat Warning until 8 PM EDT this evening for SCZ045- 148>152. MARINE...None.