textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) A prolonged heat wave will maintain hot and humid conditions for the majority of the week.

- 2) Typical summertime afternoon and evening thunderstorms this week with increasing rain chances Sunday into Monday.

DISCUSSION

KEY MESSAGE 1: A prolonged heat wave will maintain hot and humid conditions for the majority of the week.

The heat is on across the low country with several observations on the humid side of the seabreeze approaching 110 to 113 mainly across the coastal strip. Given the rather impressive high pressure in place holding off most convection until later this afternoon, its is probably safe to say that most areas should reach at least advisory criteria and remain at advisory criteria for the remainder of the afternoon. Excessive heat conditions seem to be occurring right at or just east of the seabreeze where downright disgusting dewpoints in the upper 70s to near 80 are combining with air temps in the mid to upper 90s. The only relief from the heat will be any showers this afternoon but that might be hard to come by. Very little relief from the heat is expected tonight as lows will only drop into the upper 70s to low 80s and heat indices will likely remain in the mid to upper 90s well after midnight tonight, especially for the coastal areas. These warm overnight conditions could result in prolonged heat stress, especially for more vulnerable communities and those without adequate cooling overnight.

Oppressive heat and humidity will continue Thursday, Friday, and Saturday. The ridge aloft will maintain control through the end of the week, but then starts to get suppressed to the south as west to east oriented troughing drifts in from the north over the weekend. High temperatures look quite similar each day Thursday through Saturday, with widespread upper 90s and isolated instances of triple digits. Surface winds will start off each day out of the west- southwest, allowing temperatures to rise into the upper 90s. Then the sea breeze will take hold and push mid to upper 70s dewpoints inland. The result is expected to yield the highest heat indices along the coastal corridor with values well into the 105-110 degree range and some areas into the 110-115 degree range. Further inland, heat indices should mostly top out around 105. To make conditions more uncomfortable, overnight lows will likely linger in the upper 70s, and even low 80s right along the coast. For heat headlines, the configuration of the Heat Advisory and Extreme Heat Warning will be nearly identical to Wednesday with the only difference being Inland Berkeley as an advisory and not a warning. Then for Friday and Saturday, the footprint of the Heat Advisory will likely shrink and we might not even need an Extreme Heat Warning area. Also, convective coverage each afternoon does not look high enough to provide a significant disruption to the heat and humidity. Starting Sunday, and especially into next week, temperatures should cool off as a boundary sags into the region and supports increased rain chances and greater coverage of thunderstorms each day.

KEY MESSAGE 2: Typical summertime afternoon and evening thunderstorms this week.

Satellite and radar observations this afternoon have already shown some signs of convective develop along the seabreeze, mainly north of the Charleston metro across Berkeley county. Overall guidance still remains rather weak with convective development; however, given trends and the slow progression of the seabreeze a few isolated thunderstorms should be expected over the next couple of hours. Given rather warm 850 mb temps from subsidence underneath the ridge, storms may struggle and will likely focus where what outflows that do develop interact with the seabreeze. Storms should subside by early evening.

The pattern should continue to support only isolated to scattered convective coverage Thursday through Saturday, due to a lack of any notable features to drive development. There will continue to be a low end threat of an isolated severe storm or locally heavy rainfall, mainly where boundary interactions occur. As we move into Sunday and next week, a pattern change looks to be on the horizon. The upper ridge is expected to get suppressed to the south as a west to east trough drops in from the north. This should bring a front into the area which will linger for a few days. Increased convective coverage is expected, which will hopefully bring beneficial rains to the area and possibly even some risk of locally excessive rainfall.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

VFR conditions should prevail across the area through most of the forecast. Winds have remained light out of the southwest; except behind the seabreeze where some gustier conditions to around 20 knots are possible out of the south-southwest. Combination of satellite and radar observations shows some isolated showers and thunderstorms have begun to develop along the seabreeze interface mainly in the vicinity of KCHS. Winds and storms should relax during the early evening with VFR conditions prevailing for the remainder of the overnight and morning hours.

Extended Aviation Outlook: Mostly VFR. There will be a low end risk of thunderstorm impacts each afternoon and evening, primarily at KCHS and KSAV.

MARINE

Today through tonight: Overall pattern that has been in place should remain in place with south-southwest winds between 10 to 15 kts, with occasional gusts into the low 20 kts. Wave heights are forecast to favor 3 to 4 ft.

Thursday through Monday: The overall pattern will be on repeat Thursday through Saturday as southwest flow surges each afternoon and evening. Wind speeds should solidly reach the 15-20 knot range each day, with gusts approaching 25 knots along the SC coast and the adjacent coastal waters. Seas should mostly be in the 2-4 ft range, but could rise up to around 5 ft during times of peak surging in the evening hours. It is possible that short duration Small Craft Advisories could be needed, mainly for the SC waters and the Charleston Harbor. Then by Sunday, and especially Monday, conditions should feature lower wind speeds as a boundary drops into the area from the north.

CLIMATE

Record High Temperatures:

July 8: KCHS: 100/2016 KSAV: 101/2010

July 9: KCXM: 99/1986

July 10: KCHS: 100/1986 KCXM: 99/1986 KSAV: 102/1879

July 11: KCXM: 100/2001

July 12: KCXM: 97/1966

Record High Minimum Temperatures:

July 8: KCXM: 83/2016 KSAV: 80/1990

July 9: KCHS: 80/1998 KCXM: 85/1998 KSAV: 80/1883

July 10: KCHS: 81/1986 KCXM: 82/1986

July 11: KCHS: 80/2016 KCXM: 82/2016

July 12: KCHS: 79/2020

CHS WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory until 7 PM EDT this evening for GAZ099>101-114- 115-137-216-238-240. Extreme Heat Warning until 7 PM EDT this evening for GAZ217>219-239-241. SC...Heat Advisory until 7 PM EDT this evening for SCZ043-044-147. Extreme Heat Warning until 7 PM EDT this evening for SCZ045- 148>152. MARINE...None.