Sea Ledger, April 2021

2021-04-01 to 2021-04-30 · archive

issued: 675
warning-days in force: 10,083
in force at month end: 313
sea × type cells: 222

baseline: same month, previous 5 years (2020-04, 2019-04, 2018-04, 2017-04, 2016-04)

By type

type	issued	warning-days	in force at end
Exercises	170	1,733.4	41
Icebergs	91	101	4
Surveys	86	2,014.1	63
Incidents	79	618.5	15
Nav aids	70	2,493.3	90
Missiles	48	341.5	11
Quakes	35	103.2	3
Cable ops	33	510.1	15
Other	15	388.6	13
Debris	13	29.8	1
Spills	13	166	6
Derelicts	11	132.6	4
Piracy	4	28	0
Wrecks	2	1,087.1	36
Structures	2	36.7	1
Volcanic	2	109.9	4
Mines	1	39.4	1
Restricted	0	90	3
Ordnance	0	60	2

By sea and type · 200 cells, most issued first

cell	issued	warning-days	at end	longest d	vs 5 y
Icebergs · Labrador Seasurge	30	34.1	2	31	2.0× / 14.8
Icebergs · South Atlantic Ocean	30	29.9	1	30	1.9× / 16.2
Icebergs · Southern Ocean	28	28	1	30	1.1× / 26.6
Exercises · North Pacific Ocean	24	264.2	11	50	1.1× / 22.2
Exercises · Black Sea	21	320.4	6	65	1.9× / 11.2
Surveys · South Atlantic Ocean	19	249.1	7	102	1.1× / 17.4
Incidents · South China Sealong running	18	154.7	6	389	0.7× / 25.4
Exercises · Arabian Seasurge	18	111.1	3	35	2.4× / 7.6
Quakes · South Pacific Ocean	16	46.2	3	31	1.9× / 8.4
Nav aids · South Atlantic Ocean	14	239.4	11	186	1.3× / 10.6
Exercises · Mediterranean Sea - Eastern Basin	14	85.1	0	—	0.9× / 15.2
Exercises · South Pacific Oceansurge	13	69	1	35	2.2× / 5.8
Surveys · North Atlantic Ocean	12	358.9	11	120	1.8× / 6.6
Incidents · North Pacific Ocean	12	52.6	0	—	0.6× / 21.2
Missiles · North Atlantic Oceansurge	11	46.2	1	28	2.0× / 5.4
Surveys · Arabian Sea	10	203	6	51	1.3× / 7.6
Exercises · Bay of Bengal	10	78.6	2	31	1.4× / 7
Incidents · Indian Oceansurge	10	47.7	0	—	2.2× / 4.6
Exercises · Mediterranean Sea - Western Basinsurge	10	46.1	0	—	6.3× / 1.6
Cable ops · Irish Sea and St. George's Channelsurge	10	14.1	0	—	25× / 0.4
Exercises · Aegean Sea	9	230.7	6	108	1.1× / 8.4
Exercises · South Atlantic Ocean	9	160.6	3	50	1.7× / 5.2
Nav aids · Coral Sea	9	80.7	6	39	1.1× / 7.8
Missiles · Black Sea	8	104.6	6	32	1.8× / 4.4
Cable ops · North Atlantic Oceansurge	8	57	3	30	2.2× / 3.6
Exercises · Yellow Sea	8	54.5	1	35	1.3× / 6.4
Nav aids · South Pacific Oceanlong running	7	249.3	8	907	1.8× / 3.8
Surveys · Indian Oceansurge	7	115.2	5	73	5.8× / 1.2
Missiles · Japan Seasurge	7	65.9	1	37	2.5× / 2.8
Missiles · Indian Oceansurge	7	29.6	1	28	5.0× / 1.4
Nav aids · North Pacific Oceansurgelong running	6	187.7	6	637	2.0× / 3
Surveys · Persian Gulf	6	108.7	4	102	1.3× / 4.8
Nav aids · Mediterranean Sea - Western Basinsurge	5	125.4	5	334	13× / 0.4
Incidents · Laccadive Seasurge	5	63.5	2	42	13× / 0.4
Spills · Gulf of Mexico	5	56	2	43	0.9× / 5.6
Surveys · North Seasurge	5	46.6	3	18	3.1× / 1.6
Incidents · South Atlantic Ocean	5	26.8	1	40	0.7× / 7.4
Cable ops · South Pacific Oceansurge	5	9.6	1	9	8.3× / 0.6
Incidents · Coral Sea	5	0.5	0	—	1.0× / 4.8
Nav aids · North Atlantic Oceanlong running	4	271	10	629	0.6× / 6.6
Surveys · Black Seasurge	4	184.2	6	175	3.3× / 1.2
Nav aids · North Sea	4	173.9	4	215	0.5× / 7.8
Cable ops · Mediterranean Sea - Western Basinsurge	4	51.7	0	—	4.0× / 1
Nav aids · English Channel	4	50.8	2	44	1.8× / 2.2
Surveys · Bay of Bengal	4	48.1	2	24	1.8× / 2.2
Exercises · North Atlantic Ocean	4	40.5	2	85	1.0× / 4
Exercises · Andaman or Burma Seasurge	4	15.9	0	—	3.3× / 1.2
Exercises · Mozambique Channelnew	4	15.9	0	—	new / 0
Derelicts · South Pacific Ocean	4	14.7	1	27	1.7× / 2.4
Quakes · Bismarck Seasurge	4	12	0	—	20× / 0.2
Quakes · Indian Ocean	4	12	0	—	1.5× / 2.6
Debris · Tasman Seanew	4	8	0	—	new / 0
Debris · Coral Seasurge	4	6.8	0	—	6.7× / 0.6
Nav aids · Gulf of Mexico	3	121.1	5	146	1.1× / 2.6
Incidents · North Atlantic Ocean	3	73.3	1	43	0.3× / 9.4
Nav aids · Irish Sea and St. George's Channelsurge	3	42.7	2	27	3.8× / 0.8
Spills · North Atlantic Ocean	3	37	2	39	1.1× / 2.6
Incidents · Caribbean Sea	3	34.5	2	25	1.1× / 2.6
Exercises · Laccadive Seasurge	3	34.3	1	31	2.5× / 1.2
Spills · North Pacific Ocean	3	34	1	42	1.1× / 2.8
Missiles · Barentsz Sea	3	26.9	0	—	0.7× / 4.4
Exercises · Barentsz Seasurge	3	25	0	—	2.1× / 1.4
Incidents · South Pacific Ocean	3	15.8	0	—	0.5× / 6.6
Exercises · Adriatic Seasurge	3	10.7	0	—	5.0× / 0.6
Quakes · North Pacific Ocean	3	9	0	—	0.6× / 5
Nav aids · Caribbean Sea	2	297.2	11	200	2.0× / 1
Surveys · Mediterranean Sea - Eastern Basin	2	122.6	4	123	0.4× / 5
Cable ops · Arabian Sea	2	82.4	3	102	1.1× / 1.8
Surveys · Barentsz Sea	2	47.3	3	105	10× / 0.2
Nav aids · Inner Seas off the West Coast of Scotlandlong running	2	38.5	1	505	0.6× / 3.4
Other · North Pacific Ocean	2	33.1	2	28	2.5× / 0.8
Surveys · Ionian Seanew	2	32.5	0	—	new / 0
Surveys · Mediterranean Sea - Western Basin	2	23.1	1	25	2.0× / 1
Other · Japan Sea	2	20.3	0	—	10× / 0.2
Volcanic · Caribbean Sea	2	19.9	1	19	10× / 0.2
Exercises · Caribbean Sea	2	18.4	0	—	2.5× / 0.8
Surveys · Mozambique Channelnew	2	18.2	1	23	new / 0
Incidents · Philippine Sea	2	14.3	1	44	0.6× / 3.2
Piracy · Gulf of Guinea	2	14	0	—	0.4× / 5
Piracy · Singapore Straitnew	2	14	0	—	new / 0
Exercises · Japan Sea	2	12.4	0	—	10× / 0.2
Other · Black Sea	2	12	0	—	10× / 0.2
Missiles · North Pacific Ocean	2	11	0	—	0.4× / 4.8
Exercises · Red Sea	2	10.2	0	—	3.3× / 0.6
Missiles · Gulf of Mexiconew	2	7	1	6	new / 0
Quakes · Philippine Sea	2	6	0	—	0.5× / 3.8
Debris · Timor Sea	2	6	0	—	10× / 0.2
Structures · South Atlantic Ocean	2	5.7	0	—	10× / 0.2
Missiles · South Pacific Ocean	2	3.8	0	—	0.7× / 2.8
Exercises · Bering Sea	2	3.2	1	2	10× / 0.2
Derelicts · Indian Ocean	2	3.2	0	—	0.5× / 3.8
Debris · Bay of Bengalnew	2	2.6	1	2	new / 0
Other · English Channel	2	2.3	0	—	3.3× / 0.6
Missiles · Mediterranean Sea - Western Basinnew	2	1.9	0	—	new / 0
Incidents · Arafura Sea	2	1.3	0	—	2.5× / 0.8
Cable ops · North Pacific Ocean	1	108.6	3	241	1.7× / 0.6
Surveys · South Pacific Oceanlong running	1	86.9	2	576	0.4× / 2.6
Nav aids · Arabian Sea	1	64.6	3	116	0.8× / 1.2
Nav aids · Mozambique Channel	1	64.6	3	198	new / 0
Other · Gulf of Mexico	1	55	2	109	5.0× / 0.2
Incidents · Java Sealong running	1	45	1	417	0.8× / 1.2
Cable ops · South China Sea	1	43.9	1	72	0.7× / 1.4
Nav aids · Arafura Sea	1	31.7	1	65	1.3× / 0.8
Nav aids · Indian Ocean	1	30	1	35	0.6× / 1.6
Surveys · North Pacific Ocean	1	28.9	0	—	1.3× / 0.8
Surveys · Great Australian Bight	1	28.8	1	56	1.7× / 0.6
Incidents · Arabian Sea	1	28.5	1	39	0.8× / 1.2
Surveys · Caribbean Sea	1	28.4	0	—	1.0× / 1
Other · Bering Sea	1	25.9	1	66	new / 0
Surveys · Celtic Sea	1	25.3	0	—	2.5× / 0.4
Spills · The Coastal Waters of Southeast Alaska and British Columbia	1	25	1	33	2.5× / 0.4
Other · Arafura Sea	1	23.8	1	23	new / 0
Surveys · Tasman Sea	1	22.6	1	22	2.5× / 0.4
Incidents · Mediterranean Sea - Western Basin	1	19.7	0	—	1.7× / 0.6
Surveys · Philippine Sea	1	15.5	0	—	5.0× / 0.2
Nav aids · Black Sea	1	15.4	1	15	new / 0
Incidents · Gulf of Thailand	1	15.4	0	—	0.7× / 1.4
Surveys · Japan Sea	1	14.4	0	—	new / 0
Spills · Gulf of Alaska	1	14	0	—	0.8× / 1.2
Other · Sea of Okhotsk	1	13.8	0	—	5.0× / 0.2
Other · Mozambique Channel	1	11.6	1	11	2.5× / 0.4
Incidents · Timor Sea	1	10.3	0	—	1.7× / 0.6
Mines · English Channel	1	9.4	0	—	new / 0
Other · South Pacific Ocean	1	9.2	0	—	2.5× / 0.4
Missiles · Arctic Ocean	1	6.2	0	—	5.0× / 0.2
Cable ops · South Atlantic Ocean	1	6	0	—	0.8× / 1.2
Cable ops · Tyrrhenian Sea	1	5.8	0	—	new / 0
Missiles · Baffin Bay	1	5.4	0	—	1.0× / 1
Nav aids · Celtic Sea	1	5	0	—	1.0× / 1
Surveys · Norwegian Sea	1	3.8	1	3	0.6× / 1.8
Quakes · Arabian Sea	1	3	0	—	5.0× / 0.2
Quakes · Banda Sea	1	3	0	—	0.7× / 1.4
Quakes · Celebes Sea	1	3	0	—	5.0× / 0.2
Icebergs · Chukchi Sea	1	3	0	—	new / 0
Derelicts · Gulf of Aden	1	3	0	—	new / 0
Debris · Gulf of Mexico	1	3	0	—	5.0× / 0.2
Icebergs · Gulf of St. Lawrence	1	3	0	—	2.5× / 0.4
Icebergs · Kara Sea	1	3	0	—	1.0× / 1
Derelicts · Norwegian Sea	1	3	0	—	new / 0
Quakes · Persian Gulf	1	3	0	—	5.0× / 0.2
Derelicts · South Atlantic Ocean	1	3	0	—	0.8× / 1.2
Quakes · South Atlantic Ocean	1	3	0	—	0.6× / 1.6
Quakes · Southern Ocean	1	3	0	—	new / 0
Derelicts · Timor Sea	1	3	0	—	5.0× / 0.2
Incidents · Bismarck Sea	1	2.5	0	—	1.3× / 0.8
Exercises · Persian Gulf	1	2.3	0	—	new / 0
Missiles · Laccadive Sea	1	1.9	0	—	1.0× / 1
Exercises · North Sea	1	1.8	0	—	new / 0
Exercises · Norwegian Sea	1	1.3	0	—	2.5× / 0.4
Incidents · Labrador Sea	1	1.2	0	—	5.0× / 0.2
Missiles · South China Sea	1	1.1	0	—	1.3× / 0.8
Exercises · Gulf of Oman	1	1	0	—	new / 0
Incidents · Black Sea	1	0.7	0	—	2.5× / 0.4
Wrecks · North Sea	1	0.5	1	0	0.6× / 1.8
Derelicts · South China Sea	1	0.4	0	—	1.0× / 1
Wrecks · Barentsz Sea	1	0.2	0	—	new / 0
Nav aids · Bering Sea	1	0.2	0	—	new / 0
Exercises · Philippine Sea	1	0.2	0	—	0.4× / 2.8
Incidents · Great Australian Bight	1	0.1	0	—	5.0× / 0.2
Other · Indian Ocean	1	0.1	0	—	1.7× / 0.6
Incidents · Molukka Sea	1	0.1	0	—	5.0× / 0.2
Incidents · Tasman Sea	1	0	0	—	1.0× / 1
Wrecks · Persian Gulflong running	0	270	9	501	0.0× / 0.2
Wrecks · South China Sealong running	0	270	9	803	0.0× / 1.6
Wrecks · North Atlantic Oceanlong running	0	120	4	830	0.0× / 0.2
Exercises · Ionian Sea	0	90	3	108	0.0× / 0.4
Other · Persian Gulf	0	90	3	298	0.0× / 0.2
Nav aids · Andaman or Burma Sea	0	69.5	2	116	0.0× / 1
Nav aids · Persian Gulflong running	0	68.2	1	380	0.0× / 0.6
Wrecks · South Atlantic Ocean	0	65.9	2	102	0.0× / 1
Derelicts · Arabian Sealong running	0	60	2	462	0.0× / 0.2
Wrecks · Arabian Sealong running	0	60	2	584	0.0× / 1.2
Surveys · Arctic Ocean	0	60	2	193	— / 0
Wrecks · Inner Seas off the West Coast of Scotland	0	60	2	203	— / 0
Wrecks · North Pacific Oceanlong running	0	60	2	757	0.0× / 0.6
Ordnance · North Sealong running	0	60	2	564	0.0× / 1.8
Volcanic · Philippine Sea	0	60	2	133	0.0× / 0.4
Restricted · South Atlantic Oceanlong running	0	60	2	484	0.0× / 0.2
Nav aids · Laccadive Sea	0	45.5	1	63	0.0× / 1
Nav aids · Bay of Bengal	0	44.4	1	324	0.0× / 1.4
Surveys · Irish Sea and St. George's Channel	0	32.9	1	36	— / 0
Other · North Atlantic Ocean	0	31.5	1	46	0.0× / 6.4
Cable ops · Aegean Sea	0	30	1	137	0.0× / 0.2
Missiles · Aegean Sea	0	30	1	108	— / 0
Surveys · Bering Sea	0	30	1	191	0.0× / 0.2
Cable ops · Black Sea	0	30	1	94	— / 0
Cable ops · Caribbean Sea	0	30	1	154	0.0× / 0.2
Derelicts · Caribbean Sea	0	30	1	31	0.0× / 0.8
Wrecks · Caribbean Sea	0	30	1	38	0.0× / 0.6
Other · Coral Sea	0	30	1	38	0.0× / 0.2
Wrecks · English Channel	0	30	1	112	0.0× / 0.4
Nav aids · Gulf of California	0	30	1	73	0.0× / 0.2
Nav aids · Gulf of Thailandlong running	0	30	1	561	— / 0
Wrecks · Japan Sea	0	30	1	99	— / 0
Nav aids · Mediterranean Sea - Eastern Basin	0	30	1	267	0.0× / 0.2
Other · Mediterranean Sea - Eastern Basin	0	30	1	218	0.0× / 1
Volcanic · Mozambique Channellong running	0	30	1	575	— / 0
Nav aids · Norwegian Sea	0	30	1	49	0.0× / 0.4
Cable ops · Persian Gulf	0	30	1	159	0.0× / 0.4
Mines · Persian Gulf	0	30	1	117	— / 0

Cite: seahazards.com Sea Ledger, 2021-04, retrieved 2026-09-03

Not for navigation. Warning-days = days each warning was in force within the month, summed. Only warnings we display are counted; the ratio compares warnings issued with the mean of the reference months.