Fort McHenry Marsh, MD

The next high tide at Fort McHenry Marsh is at 9:33 pm local time, reaching 1.87 ft above MLLW. The next low tide is tomorrow at 4:53 am (0.63 ft).

Fort McHenry Marsh has mixed semidiurnal tides, which means two highs and two lows a day of noticeably different sizes. This week the paired highs differ by 0.6 ft on average and the lows by 0.3 ft. Times shift roughly 50 minutes later each day as the moon advances, which is why a printable weekly or monthly table is more useful than a single day's times.

The lowest tide at Fort McHenry Marsh in the next seven days is 0.29 ft at 2:37 pm on 2026-10-13. The highest is 1.87 ft at 9:33 pm on 2026-10-13.

Slack water, when the current is weakest, falls roughly midway between a high and a low. Today that is around 6:25 am, 11:42 am, 6:05 pm. These are estimates from the tide times; true slack can lag the turn by up to an hour in a narrow channel or river mouth.

Tides here are currently between spring and neap. The moon is waxing crescent (8% illuminated). Spring tides, the biggest range between high and low, follow the new and full moon, when the sun and moon pull in line. Neap tides, the smallest range, follow the quarter moons.

Today's range is 1.6 ft between the highest high and the lowest low. The average daily range here over the next month is about 1.4 ft, so today is typical.

The lowest tide today at Fort McHenry Marsh is at 2:37 pm at 0.29 ft above MLLW. The lowest predicted tide over the next month at Fort McHenry Marsh is 0.06 ft.

The rule of twelfths estimates how much water moves in each hour of a roughly six-hour tide: 1/12 of the range in the first hour, then 2/12, 3/12, 3/12, 2/12 and 1/12. Water moves fastest in the middle two hours and barely moves near high and low slack. With Fort McHenry Marsh's range today of about 1.6 ft, that is roughly 0.1 ft in the first hour and about 0.4 ft during each of the two middle hours.

Most inshore anglers prefer moving water rather than slack tide, so the two hours either side of a high or low, when the rule of twelfths says flow is fastest, tend to fish best. Using today's predictions, the strongest movement is between 4:02 am and 8:48 am. Local conditions, wind and season matter as much as the tide itself.

Low tide exposes the most sand and the widest walking beach, and is best for tidepooling and shelling. High tide suits swimming and launching boats, though it leaves less dry beach. At Fort McHenry Marsh the difference between the two is about 1.6 ft of water height.

"Rule of 6" is another name for the rule of twelfths above. It is the idea that a tide takes about six hours to run, and that the water moves by a different fraction of its range in each of those six hours. Some people also use it as shorthand for the roughly six-hour gap between a high and the next low, which at Fort McHenry Marsh averages about 6.0 hours today.

The tide times on this page are NOAA's astronomical predictions for station 8574683, typically within about 10 minutes on timing and half a foot on height. They account for the sun and moon but not the weather. A strong onshore wind, a storm surge or unusually high or low barometric pressure can push the real water level well above or below the prediction. Never use them for navigation or life-safety decisions. NOAA's own page for this station carries the official record.

All heights are feet above mean lower low water (MLLW), the standard NOAA tidal datum for US coastal predictions, the average of the lower of the two daily low tides. A reading of 0.0 ft means water at that reference level, and a negative reading means below it.

The nearest water-temperature reading to Fort McHenry Marsh is 82 °F (27.7 °C), measured 3:00 pm at NDBC buoy BLTM2, 0 miles away. It has risen 7.2 °F in the last 24 hours.