JMA Weather Station Guide: AMeDAS & Observatory Data, JST Rules & Excel Export

Guide to Japan Meteorological Agency (JMA) surface observations: compare AMeDAS and observatory stations across 10-minute to monthly timescales, reconcile JST observation hours, and export Excel workbooks.

1. Home
2. Guides
3. JMA guide

Open the JMA Explorer

Current JMA Explorer map with daily stations around Tokyo

Quick start

1. Open the explorer and choose 10 Minutes, Hourly, Daily or Monthly.
2. Set a date range, then find a station on the map or in Station Info.
3. Open Dashboard and check both Plots and Data.
4. Select Export Excel to download the current parsed table as an .xlsx workbook.

The explorer is an independent interface for observations produced and published by the Japan Meteorological Agency (JMA). Climate Explorer retrieves and parses selected JMA historical tables; it does not produce the observations and is not affiliated with or endorsed by JMA.

1. Choose the right station family

JMA’s Past Weather Data Search uses different table families for surface observatories and AMeDAS sites. Their URLs commonly contain s1 or a1, respectively. This distinction matters because the source columns are not identical.

JMA historical source-table families

Source-table family	What it represents in this guide	Typical distinction
s1	Surface-observatory tables	Can expose a broader set of elements, such as pressure, humidity and some visually observed fields.
a1	AMeDAS tables	Automated sites; the available combination of precipitation, temperature, wind, humidity and snow depends on the site.

The explorer may display the source grouping as AMeDAS or Manned station. Treat that as a portal/table classification, not proof that a person currently staffs a particular site. JMA’s surface-observation overview explains that both manned and unmanned surface stations use automatic observing equipment.

2. Set resolution and dates

The left sidebar controls the resolution, station search and requested period.

Current JMA Explorer request limits

Resolution	Useful for	Maximum period per request
10 Minutes	Short-duration changes	93 days
Hourly	Within-day patterns	93 days
Daily	Daily summaries	366 days
Monthly	Longer summaries	1,826 days, or about five years

These are Climate Explorer request limits, not statements about the full length of JMA’s archive. Change the dates and repeat the export when you need a longer period. Record availability still depends on the selected station and variable.

JMA source tables use Japan Standard Time (JST). If an hourly source row uses hour 24, interpret it as the end of that Japanese civil day before converting timestamps to another time zone.

Observation Hours: The 9:00 to 9:00 JST Daily Precipitation Rule

When analyzing precipitation records across different tools, international climate databases, or research publications, you may encounter two distinct definitions of a “daily” precipitation total:

1. JMA Portal & AMeDAS Daily Tables (Civil Day: 00:00 to 24:00 JST): In JMA’s domestic digital portals (including the daily_a1.php and daily_s1.php tables accessed by Climate Explorer), the daily precipitation total (日降水量) aggregates rainfall over the local Japanese civil calendar day—from 00:01 to 24:00 JST (midnight to midnight). Each hourly value in JMA tables represents the accumulation during the preceding 60 minutes ending at that hour.

2. The Synoptic and Climatological Observation Day (9:00 to 9:00 JST): Under World Meteorological Organization (WMO) synoptic reporting standards and historical climatological practice, the 24-hour meteorological observation day runs from 00:00 UTC to 24:00 UTC. Because Japan Standard Time is fixed at UTC+9 without daylight saving time, midnight UTC corresponds to 09:00 AM JST. A synoptic daily precipitation total recorded at 09:00 JST represents the rainfall accumulated over the 24-hour window from 09:00 JST on the previous calendar day to 09:00 JST on the observation date.

Why this 9-hour phase offset matters:

• Attribution of morning rainfall: Heavy rain falling between midnight and 09:00 JST belongs to calendar day D in JMA daily tables and Climate Explorer daily exports, but is counted as part of the observation day ending at 09:00 JST on day D (corresponding to day D−1 in UTC-based archives).
• International dataset alignment: Global climatological databases (such as NOAA GHCN-Daily, WMO CLIMAT bulletins, and international reanalyses) ingest Japanese synoptic observations aligned to the 00:00 UTC day. Consequently, daily precipitation values reported in NOAA GHCN or WMO summaries will not match JMA’s domestic calendar-day totals for the same nominal date.
• Historical manual day boundaries (Ninkai): In historical manual observations before modern automated AMeDAS telemetry, Japanese weather stations performed manual rain gauge readings at 09:00 JST. Long-term historical studies must account for this day boundary (ninkai / 日界) to avoid artificial step-changes when stitching historical manual logs with modern digital series.

Reconciling JMA Daily Data with 00:00 UTC Archives

If your research requires 24-hour totals strictly aligned to 00:00 UTC (9:00 AM to 9:00 AM JST):

1. Select Hourly resolution in the JMA Explorer rather than Daily.
2. Export the hourly series for your target window (including one extra day).
3. Sum the 24 consecutive hourly observations from hour 10 of day D−1 through hour 9 of day D.

3. Find and verify a station

Map View

The map filters station markers using the current resolution and dates. Select a marker to see its name, identifier, source grouping and record summary. The sidebar’s Find Station control is faster when you already know a name.

Do not use the visible-station count as a fixed network total. It changes with the selected resolution, dates and current metadata.

Station Info

Current Station Info table in the JMA Explorer

Use Station Info to check metadata before requesting observations. The table can show:

• JMA block identifier;
• English and Japanese names;
• prefecture;
• latitude, longitude and elevation;
• variables associated with the station; and
• start and end dates by resolution.

Double-click a row to select the station and open its dashboard. If two similarly named sites appear, compare their identifier, coordinates, elevation and operating period rather than relying on the name alone.

4. Inspect plots and data

Current daily Plots view for Tokyo station 47662

The Dashboard header records the selected station, location, elevation, resolution and dates. Confirm these before interpreting or exporting results.

The Plots view summarizes only fields present in the returned table. Depending on station and resolution, panels can include temperature, precipitation, wind, humidity, pressure, sunshine or snow. A missing panel does not necessarily mean that a variable never existed; it means the current parsed selection does not provide a usable series for that panel.

Current daily Data view for Tokyo station 47662

Open Data to inspect the rows behind the plots. Use the search and pagination controls to locate dates or values. Blank cells can represent unavailable, missing or unparsed source values, so consult the official JMA table when flags or exact source notation matter.

5. Export an Excel workbook

1. Confirm the station, resolution and dates in the dashboard header.
2. Open Data and check that the expected dates and columns are present.
3. Select Export Excel.
4. Open the .xlsx file and preserve the station identifier, resolution, time zone and retrieval date with your analysis notes.

The workbook is generated by Climate Explorer from the parsed selection. It is not an official JMA bulk file and does not replace the original table, annotations or revisions.

Minimum reproducibility notes for an exported workbook

Preserve with the workbook	Why it matters
Station name and block identifier	Distinguishes similarly named or translated locations.
Resolution and requested dates	Defines the aggregation and selection window.
Japan Standard Time	Prevents accidental date shifts during conversion.
Source URL and retrieval date	Supports later verification against JMA revisions.

6. Understand the processed columns

Column availability varies by station, table family and period. These are the processed fields Climate Explorer can expose when the corresponding JMA columns are present.

Processed JMA fields and their displayed units

Processed field(s)	Display unit	Typical resolution(s)	Interpretation
Year, Month, Day, Hour, Time	JST components	all	Source-table date and time components. Interpret hour 24 before converting time zones.
Temperature	°C	10-minute, hourly	Air temperature reported for the table time
Temp_Mean, Temp_Max, Temp_Min	°C	daily, monthly	Provider-supplied period temperature summaries
Pressure, Pressure_Sea_Level	hPa	10-minute, hourly, daily, monthly	Station pressure versus pressure reduced to sea level
Precipitation	mm	all	Precipitation for the source-defined interval or period
Precipitation_Max_1h, Precipitation_Max_10min	mm	daily	Largest source-defined 1-hour and 10-minute amounts in the daily table
Humidity, Humidity_Min	%	10-minute, hourly, daily, monthly	Relative humidity and, where supplied, the period minimum
Wind_Speed, Wind_Speed_Max (Wind_Max_Speed in some daily parses)	m/s	all	Mean or instantaneous wind and the source-period maximum
Wind_Gust_Speed	m/s	daily, monthly	Maximum gust where the source table provides one
Wind_Direction, Wind_Direction_Deg	text or degrees	all	Compass text or numeric direction; availability depends on the table
Sunshine_Minutes, Sunshine_Hours	min at 10-minute; h otherwise	all	Sunshine duration, with a resolution-dependent processed field and display unit
Solar_Radiation	MJ/m²	daily, monthly	Integrated solar-radiation energy where observed
Snowfall, Snow_Depth	cm	daily, monthly	New snowfall and snow lying are separate fields
Snow_Days, Fog_Days, Thunder_Days	days	monthly	Counts of days with the named phenomenon
Dew_Point, Vapor_Pressure	°C, hPa	daily, monthly	Moisture variables available in some observatory tables
Cloud_Cover, Visibility	tenths, km	daily, monthly	Total cloud amount and visibility where supplied

The same processed name can represent a different aggregation at 10-minute, hourly, daily or monthly resolution. JMA’s s1 and a1 table families can also expose different elements and source notation. Read the original heading, annotations and unit before combining exports; the workbook contains only fields successfully parsed from the selected table.

7. Troubleshoot common problems

No stations match the filters

Shorten or move the date range, try another resolution, or clear the station search. A station can have daily records without having the same period at 10-minute resolution.

A request returns no rows

Verify that the selected dates fall within the station’s period for that resolution. Then shorten the request. JMA can also revise or temporarily change source pages, so confirm the same selection in the official portal.

A variable or chart is missing

Check Station Info and the Data columns. Equipment differs across station families and sites, and the available elements can change through time.

The exported date appears shifted

Retain JST until you have interpreted any source hour 24 value. Convert to UTC or another zone only after constructing the correct local date-time.

You need authoritative flags or documentation

Open the corresponding JMA Past Weather Data Search table. Climate Explorer translates and normalizes selected fields for convenience, which can omit source-page notation.

8. Choose the next page

• Use the JMA Explorer for broad station discovery and interactive comparison.
• Read How JMA’s AMeDAS and Observatory Tables Differ for the evidence-led explanation of why fields vary between JMA table families.

Official sources and terms

• JMA Past Weather Data Search
• JMA Historical Weather Data Download
• JMA AMeDAS overview
• JMA Surface Observation overview
• JMA website terms of use

JMA’s terms require source attribution when its website content is reused. They also note that content can be modified, moved or deleted without prior notice. Check the current terms for your use case.