The warning system and message format

HYDROPAC

The U.S. long-range warning series for the Pacific outside NAVAREA XII and for the Indian Ocean, Persian Gulf and adjoining seas.

HYDROPAC is the counterpart of HYDROLANT for the Pacific and Indian Oceans. The National Geospatial-Intelligence Agency issues HYDROPACs for waters outside NAVAREA XII, the eastern North Pacific area the United States coordinates. A large share of the rocket-launch and space-debris areas in this archive, and many of the South China Sea and Persian Gulf notices, arrived as HYDROPACs.

Like the other NGA series, a HYDROPAC is numbered through the year (HYDROPAC 2436/23) and stays in force until a later message cancels it or its own cancellation time passes.

What the archive shows

23,501 messages in this archive use “HYDROPAC”, the earliest issued 1948-05-27 and the latest 2026-09-23. 11 of them are in force in the latest lists we collected. A hazard reported again and again counts once per message.

The largest yearly count is 2017, with 1,440 messages. Collection is incomplete between 2024-05 and 2026-08-17, so 2024, 2025 and 2026 are not comparable with fully collected years.

Other accounts for 13,111 of 23,501 recorded messages (56%), the largest warning type group in this selection.

Located messages that use it fall in 56 sea areas; the most frequent are South Pacific Ocean (832), South China Sea (825) and Indian Ocean (738).

Its use is spread fairly evenly through the year: the busiest month, January, has 2,154 messages and the quietest, June, 1,790.

By warning series: HYDROPAC 23,454, HYDROLANT 27, NAVAREA XII 12 and HYDROARC 3, and 2 more.

Messages using it, by year of issue

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'24
'25
'26

By month of issue, all years

Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Where it appears · 56 sea areas

In force now · 11

  1. HYDROPAC 2700/26 · Surveys · Bering Sea2026-09-17 · in force

    …MOORING, AT DEPTH SEVEN METERS, ESTABLISHED IN 66-19.59N 168-57.01W. 2. CANCEL HYDROPAC 1795/25.

    Scientific mooring, at depth seven meters, established in 66-19.59N 168-57.01W →
  2. HYDROPAC 2238/26 · Nav aids · South Pacific Ocean2026-08-05 · in force

    …CHILE. 1. MAGALLANES RADIO 53-09.90S 070-54.30W HF, MF AND RADIOTELEX OFF AIR. 2. CANCEL HYDROPAC 527/26.

    Magallanes radio 53-09.90S 070-54.30W hf, mf and radiotelex off air →
  3. HYDROPAC 2092/26 · Derelicts · Arabian Sea2026-07-21 · in force

    ARABIAN SEA. INDIA. 1. DERELICT M/V AL JAFZIA AGROUND IN 19-11.50N 072-46.40E. 2. CANCEL HYDROPAC 1624/26.

    Derelict M/V al jafzia aground in 19-11.50N 072-46.40E →
  4. HYDROPAC 2039/26 · Volcanic · North Pacific Ocean2026-07-16 · in force

    …VOLCANIC ACTIVITY REPORTED IN VICINITY 20-26.00N 145-01.00E AT 160013Z JUL. 2. CANCEL HYDROPAC 153/24.

    Discolored water with increased likelihood of submarine volcanic activity reported in vicinity 20-26.00N… →
  5. HYDROPAC 2011/26 · Surveys · Timor Sea2026-07-14 · in force

    …12-22.00S 126-01.00E, 11-30.00S 126-01.00E. TWO MILE BERTH REQUESTED. 2. CANCEL HYDROPAC 1694/26.

    Survey operations in progress until further notice by M/V shark 1 in area bound by 11-30.00S 125-05.00E,… →
  6. HYDROPAC 1978/26 · Storms · Philippine Sea2026-07-10 · in force

    …INFORMATION CAN BE FOUND AT HOMEPORT.USCG.MIL USING THE PORT DIRECTORY TAB. 5. CANCEL HYDROPAC 1947/26.

    Due to tropical storm bavi: 1. the following port(s) are closed: a. rota island 14-08.35N 145-08.09E →

How it reads in recent messages

  1. HYDROPAC 2761/26 · Missiles2026-09-23

    …170-10.00E, 28-28.00N 164-59.00E, 26-39.00N 156-15.00E, 23-28.00N 144-48.00E. 2. CANCEL HYDROPAC 2749/26. 3. CANCEL THIS MSG 041933Z OCT 26.

    Hazardous operations, space debris 1427Z to 1833Z daily 28 sep thru 04 oct in area bound by 23-55.00N… →
  2. HYDROPAC 2746/26 · Exercises · Bay of Bengal2026-09-22

    …080-46.00E, 12-59.00N 080-46.00E, 12-59.00N 081-26.00E, 12-49.00N 081-26.00E. 2. CANCEL HYDROPAC 2732/26. 3. CANCEL THIS MSG 301230Z SEP 26.

    Hazardous operations 0130Z to 1130Z daily 24 thru 30 sep in area bound by 12-49.00N 080-46.00E, 12-59.00N… →
  3. HYDROPAC 2743/26 · Surveys · Arabian Sea2026-09-22

    …072-19.25E, 18-29.63N 072-19.12E, 18-29.78N 072-10.39E. WIDE BERTH REQUESTED. 2. CANCEL HYDROPAC 2677/26. 3. CANCEL THIS MSG 160001Z OCT 26.

    Survey operations in progress by kohinoor 1 until 12 oct, and M/V fugro mapper until 15 oct in areas bounded… →
  4. HYDROPAC 2741/26 · Surveys · Indian Ocean2026-09-22

    …20-35.47S 115-43.80E, 20-19.72S 115-43.80E. TWO MILE BERTH REQUESTED. 2. CANCEL HYDROPAC 2373/26.

    Underwater operations in progress until further notice by M/V fugro kwilena in area bound by 20-19.72S… →
  5. HYDROPAC 2736/26 · Nav aids · Arafura Sea2026-09-22

    …CARPENTARIA. AUSTRALIA. 1. DUYFKEN POINT LIGHT IN 12-34.15S 141-35.98E UNLIT. 2. CANCEL HYDROPAC 2725/26.

    Duyfken point light in 12-34.15S 141-35.98E unlit →
  6. HYDROPAC 2735/26 · Cable ops · Singapore Strait2026-09-22

    …CABLESHIP PETER FABER IN VICINITY 01-16.75N 104-08.14E. WIDE BERTH REQUESTED. 2. CANCEL HYDROPAC 2683/26.

    Cable operations 23 sep until further notice by cableship peter faber in vicinity 01-16.75N 104-08.14E →
  7. HYDROPAC 2683/26 · Cable ops · South China Sea2026-09-17

    …JOINING 02-04.23N 104-47.97E, 02-04.84N 104-47.94E. WIDE BERTH REQUESTED. 2. CANCEL HYDROPAC 2642/26.

    Cable operations in progress until further notice by cableship peter faber along trackline joining 02-04.23N… →

Earliest in the archive

  1. SPECIAL 1/48 · Other1948-05-27

    …ISSUING WARNINGS AS NAVAREAS IV AND XII BROADCASTS IN ADDITION TO THE HYDROLANT AND HYDROPAC SERIES.

    Navigational warnings broadcast by nga are normally divided into categories, hydrolants and hydropacs (1),… →

Often in the same message

Related terms

NAVAREA
One of the 21 ocean areas of the World-Wide Navigational Warning Service, each with a coordinator that broadcasts long-range warnings.
HYDROLANT
The U.S. long-range warning series for Atlantic waters outside NAVAREA IV, including the eastern Atlantic, the Mediterranean and adjoining seas.
HYDROARC
The U.S. long-range warning series for the Arctic Ocean.
Rocket launching
The areas where spent rocket stages, boosters and fairings are expected to fall after a launch, with the launch window.

Counts cover the messages in this archive that use the term, recounted 2026-09-24; see coverage for what is collected and since when. Not for navigation — follow official NAVAREA and coastal broadcasts.

HYDROPAC — what it means in a navigational warning · seahazards