NHC

Integration with the National Hurricane Center providing real-time tropical cyclone advisories, position data, intensity measurements, and forecast links.

Overview

The National Hurricane Center (NHC) is a division of NOAA that provides authoritative tracking and forecasting for tropical cyclones in the Atlantic and Eastern Pacific basins. While GDACS also covers tropical cyclones globally, the NHC provides more frequent updates and detailed advisory information for storms in its coverage area.

TerraGuard polls the NHC API every 5 minutes to track active storms.

What NHC Provides

NHC data focuses exclusively on tropical cyclone systems:

Data Point	Description
Storm ID	Unique identifier (e.g., `AL052026`)
Name	Storm name (e.g., "Maria")
Classification	Storm category (HU, TS, TD, STS, STD, PTC)
Intensity	Maximum sustained wind speed in knots
Pressure	Central pressure in millibars
Position	Current latitude/longitude
Movement	Direction and speed of movement
Advisory URLs	Links to public, forecast, and discussion advisories

Data Format

NHC provides an ActiveStorms JSON response listing all currently tracked tropical systems:

{
  "activeStorms": [
    {
      "id": "AL052026",
      "binNumber": "AT5",
      "name": "Maria",
      "classification": "HU",
      "intensity": 110,
      "pressure": 955,
      "latitudeNumeric": 23.4,
      "longitudeNumeric": -75.2,
      "movementDir": 315,
      "movementSpeed": 12,
      "lastUpdate": "2026-03-28T15:00:00Z",
      "publicAdvisory": {
        "issuance": "2026-03-28T15:00:00Z",
        "url": "https://www.nhc.noaa.gov/text/refresh/MIATCPAT5+shtml/..."
      },
      "forecastAdvisory": {
        "issuance": "2026-03-28T15:00:00Z",
        "url": "https://www.nhc.noaa.gov/text/refresh/MIATCMAT5+shtml/..."
      },
      "forecastDiscussion": {
        "issuance": "2026-03-28T15:00:00Z",
        "url": "https://www.nhc.noaa.gov/text/refresh/MIATCDAT5+shtml/..."
      }
    }
  ]
}

Key Properties

Property	Type	Description
`id`	string	NHC storm identifier (e.g., `AL052026`)
`name`	string	Assigned storm name
`classification`	string	Storm classification code
`intensity`	float	Maximum sustained wind speed (knots)
`pressure`	float	Central pressure (millibars)
`latitudeNumeric`	float	Current latitude
`longitudeNumeric`	float	Current longitude
`movementDir`	float	Direction of movement (degrees)
`movementSpeed`	float	Speed of movement (knots)
`lastUpdate`	ISO 8601	Last advisory issuance time
`publicAdvisory`	object	Link to public advisory text
`forecastAdvisory`	object	Link to forecast advisory
`forecastDiscussion`	object	Link to forecast discussion

Classification Codes

NHC uses specific codes for storm classifications:

Code	Name	Description
`HU`	Hurricane	Sustained winds >= 64 knots
`TS`	Tropical Storm	Sustained winds 34-63 knots
`TD`	Tropical Depression	Sustained winds < 34 knots
`STS`	Subtropical Storm	Subtropical system with storm-force winds
`STD`	Subtropical Depression	Subtropical system below storm force
`PTC`	Post-tropical Cyclone	Former tropical system

Alert Level Mapping

TerraGuard maps NHC storm intensity to alert levels using Saffir-Simpson scale thresholds:

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The specific thresholds in the adapter:

Wind Speed (knots)	Alert Level	Category
>= 137	RED	Category 5
>= 96	RED	Category 3-4 (Major Hurricane)
>= 64	ORANGE	Category 1-2
>= 34	GREEN	Tropical Storm
< 34	GREEN	Tropical Depression

How the Adapter Works

1. Polling

The adapter fetches the NHC active storms endpoint:

GET https://www.nhc.noaa.gov/CurrentStorms.json

2. Event ID Construction

NHC storm IDs are prefixed with nhc: for namespacing:

nhc:{storm_id}

For example, storm AL052026 becomes nhc:AL052026.

3. Normalization

The adapter constructs a human-readable title from the classification and name:

Classification	Name	Title
`HU`	Maria	"Hurricane Maria"
`TS`	Alberto	"Tropical Storm Alberto"
`TD`	--	"Tropical Depression [name]"

The description includes key measurements:

"Hurricane Maria with max sustained winds of 110 knots and central pressure of 955 mb"

4. Measurements Extracted

Three measurements are recorded for every storm:

Measurement	Source Field	Unit	Primary
Max wind speed	`intensity`	knots	Yes
Central pressure	`pressure`	mb	No
Movement speed	`movementSpeed`	knots	No

5. Advisory URLs

The adapter collects all available advisory URLs from the response and stores them in SourceURLs:

Key	Description
`public_advisory`	Public advisory text
`forecast_advisory`	Forecast advisory data
`forecast_discussion`	Meteorologist discussion
`windspeed_probabilities`	Wind speed probability graphics
`best_track_gis`	GIS data for the storm track
`earliest_arrival_msw`	Earliest arrival of storm-force winds
`most_likely_time_msw`	Most likely timing of storm-force winds

NHC vs. GDACS for Tropical Cyclones

Both NHC and GDACS report tropical cyclones, but they serve different purposes:

Aspect	NHC	GDACS
Coverage	Atlantic + Eastern Pacific	Global
Update frequency	Every advisory (~6 hours, more during active storms)	Every episode update
Measurements	Wind speed (knots), pressure (mb)	Wind speed (km/h)
Advisory links	Full advisory text URLs	GDACS report page
Alert level	Saffir-Simpson based	GDACS impact model based

The Event Processor's correlation pipeline handles the overlap -- when both sources report the same storm, they are correlated to the same DisasterEvent using the spatial/temporal matching with the match_by_name: true setting for tropical cyclones (150km radius, 12-hour window).

Polling Configuration

Setting	Default	Description
`NHC_ENABLED`	`true`	Enable/disable the NHC adapter
`NHC_POLL_INTERVAL`	`5m`	How often to poll the NHC API
`NHC_API_URL`	`https://www.nhc.noaa.gov/CurrentStorms.json`	API endpoint
`FETCH_TIMEOUT`	`15s`	HTTP request timeout

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