Mostly quiet week ahead, but watch the tides

/ March 17, 2019 at 11:34 PM

Weather-wise, we have a pretty tranquil week ahead (save for maybe a shower or two overnight Wednesday into Thursday morning). We’ll just need to keep an eye on tides with a full moon in perigee (“Supermoon!”) this week.

Cooler than normal to start Spring

The vernal equinox, which marks the beginning of astronomical Spring, will occur Wednesday at 5:58 PM. (Meteorologists started spring on March 1, as using months is a generally easier way to compare seasons year-to-year.)

Despite the tilt of the earth, we’ll finish out the end of astronomical winter with temperatures running well below normal. Lows could bottom out in the mid to upper 30s by mid-week, which could prompt some frost concerns depending on how the wind forecast plays out. A gradual warming trend is noted from Wednesday on, though, as surface high pressure gets situated in the Atlantic and flow turns more southerly. Early indications are that we’ve got quite a pleasant weekend lined up, with temperatures in the low 70s with ample amounts of sunshine.

We could use the rain…

U.S. Drought Monitor as of March 14, 2019. Rainfall departures are 4-6″ below normal.

Despite the fact that it seems like it rains every weekend, we are, in fact, hurting for rainfall over much of the Lowcountry. At the airport, we are running almost 5.7″ behind where we should be for this time of year. The situation isn’t much better downtown, where we are running a little over 4.8″ behind where we should be. We’ve been classified as “abnormally dry” in the weekly US Drought Monitor for the last few weeks, and this looks to continue in the absence of any wet storm systems.

The only chance of rain indicated in the forecast this week is for overnight Wednesday into early Thursday morning, where a few showers could spring up as a coastal trough develops nearby. Otherwise, it may be early next week before measurable rain returns to the forecast.

Beware the tides of March

Probabilistic surge guidance from the P-ETSS model indicates the potential for tidal flooding (tides over 7′ mean lower low water) Tuesday-Friday.

You don’t need rain for flooding in Charleston, though — a close-proximity full moon and favorable winds will get it done for you, and this week looks to be no exception. As high pressure wedges into the area from the north, winds will turn east and northeast. This, combined with a “supermoon” — essentially a full moon on its perigee (closest to Earth) — will allow for the potential for some coastal flooding Tuesday through Thursday. Guidance indicates tides could potentially reach into the moderate flood stage (over 7.5′ mean lower low water), which may cause problems with travel in downtown Charleston particularly during the Wednesday morning rush.

Keep an ear out for Coastal Flood Advisories from the National Weather Service as Tuesday gets closer. Be sure to submit your flooding reports over Twitter or using the MyCoast app, too! This data helps researchers determine how effective flood mitigation steps (such as check valves) in downtown Charleston actually are.

Other than that, though, enjoy a quiet week of more sun and increasingly warm temperatures, especially from Wednesday on.

A brief note on Twitter automation

As you may have noticed, I’ve turned on some additional automation on Twitter in the past week. This ensures a reasonable, but not overwhelming, flow of updates during this tranquil period as I continue to work on new features for @chswx. If you have any questions about an automated forecast, please let me know. If you want first crack at seeing what’s coming, consider becoming a patron of @chswx for sneak peeks and much more!

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