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May 28, 2023

Tropics Active, Potential SC Impacts This Week

by Frank Strait Aug. 27, 2023 12:00AM Key Points: A lot is going on in the tropics, including two features that will have some effects on South Carolina over this upcoming week. The breakdown follows.

by Frank Strait

Aug. 27, 2023

12:00AM

Key Points:

A lot is going on in the tropics, including two features that will have some effects on South Carolina over this upcoming week. The breakdown follows.

Franklin:

A loop of true color satellite images showing Franklin north of Puerto Rico. The forecast track and uncertainty cone are overlaid. Source: University of Wisconsin RealEarth

Franklin formed in the Caribbean Sea on Tuesday and is now north of Puerto Rico. It's a mid-range tropical storm, and it's fighting against wind shear today. It will zig-zag northward over the next week and pass west of Bermuda. This track will take it away from the strong upper-level winds shearing it. More favorable conditions will allow it to intensify, and it could be a major hurricane by Tuesday. It will pass far enough away that we won't see any wind, rain, or storm surge. However, Franklin will churn the Atlantic and send swells toward the East Coast. These swells will lead to dangerous surf on our coast and create hazardous boating conditions in our coastal waters starting Monday.

Northwestern Caribbean Disturbance:

A loop of true color visible satellite images showing a disturbance causing thunderstorms over the northwestern Caribbean Sea. Source: University of Wisconsin RealEarth

This feature is our primary concern over the next week. It looks ragged and disorganized now, but it's approaching an area favorable for tropical cyclone development. Computer models have trended toward agreement on this becoming a tropical cyclone once it reaches the eastern Gulf of Mexico on Monday. The models then indicate a northward to northeastward track across Florida and then near our coast around the middle of next week.

Uncertainty is high about this system because it hasn't begun the development process yet. However, the model consensus concerns the National Hurricane Center (NHC); they say this feature has a 70% chance of becoming a tropical cyclone. It stands to reason that there's a 30% chance that what comes toward our coast next week is a blob of disorganized thunderstorms. On the other hand, a reasonable worst-case scenario is that this could be a strong tropical storm or low-end hurricane scraping our coast next week.

Even if this turns out to be a weak system, there's a full moon next Wednesday. Heavy rain and weak to moderate onshore wind at high tide at a full moon can cause major flooding along our coast, especially in flood-prone Charleston.

Uncertainty is too high today to recommend hardcore hurricane preparation, but the situation warrants ensuring you have fully stocked disaster kits. As always, y'all can visit hurricane.sc for preparation tips.

Other Systems:

A loop of true color visible satellite images showing the eastern and central North Atlantic, where there are a few disturbances to track. Source: University of Wisconsin RealEarth

We continue to watch the remains of Tropical Storm Emily, which only existed for about 30 hours Sunday and Monday and are still being monitored by NHC for possible redevelopment. However, it has become more disorganized over the last day, and odds of this system making a comeback are down to 20 percent. It's more likely to merge with a front west of the Azores over the weekend.

A tropical wave east and northeast of the Lesser Antilles has spawned an area of low pressure near 22° north and 45° west, with some associated thunderstorms. NHC is giving this a 50 percent chance to develop over the next week. Computer models keep it out over the middle of the Atlantic, so direct impacts from it are not a concern for us, but if it gets strong enough, it could send ocean swells to our coast like Franklin will.

A new tropical wave just emerged from Africa and is along 20° west, still east of Cabo Verde. Computer models are lukewarm about development prospects for this wave, as it will be fighting with dry air and wind shear for days as it crosses the tropical Atlantic. A stronger tropical wave is crossing West Africa, and models are bullish on its prospects once it reaches the Atlantic. However, the weather pattern will favor it recurving somewhere near or east of Bermuda.

We'll also have to be on guard against more sneak attacks from disturbances originating from Central America and its vicinity during early September.

After a nice break from intense heat at midweek, we're back in the furnace and will remain there this weekend. It looks as though the 'death ridge' (a term we sometimes use to describe a persistent and sprawling upper-level ridge in the summertime that causes prolonged heat waves) over the nation's midsection is mercifully breaking down and shifting to the west, allowing cooler air from Canada to settle into the area east of the Rockies.

Through Saturday, we'll be simmering with highs in the middle to upper 90s across the Palmetto State, perhaps reaching 100 in the usual I-20 hot spots. A lucky few will enjoy a cooling afternoon thunderstorm, though any storm that does pop up can cause locally strong winds along with the usual downpours and lightning hazards.

We'll simmer again on Sunday, but a cold front will arrive late to increase our thunderstorm coverage for the afternoon and night. There is also a better chance for stronger storms with locally damaging wind.

This front will get stuck over the Carolinas early next week, resulting in a cooler and unsettled period for the start of next week. On Tuesday, some moisture and energy from the remnants of Tropical Storm Harold, which made landfall in Texas this past Tuesday and is now over Colorado, will pass through the region and give us a relatively active day.

A loop of visible satellite imagery over the continental U. S. shows clouds associated with Harold's remains over the Rockies and over the upper Midwest and Northeast associated with a cold front moving slowly southward.

Wednesday and beyond will depend on what happens with the critter trying to develop over the northwestern Caribbean Sea today. What looks most likely is a stormy Wednesday or Wednesday night for parts or all of the state, followed by a pleasant stretch of cooler and dry weather at the end of the week.

by Frank Strait

Aug. 27, 2023

12:00AM