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Tropical Cyclone Analysis and Forecast bulletins (”RSMC” bulletins)


World Meteorological Organization (WMO) header: AWIO30 FMEE

The tropical cyclone analysis and forecast bulletins (or commonly called the ”RSMC” advisories) are the most complete technical bulletins explaining the analysis and prognosis made by the tropical cyclone specialist at RSMC La Reunion. In addition to the current latitude and longitude coordinates of the centre, the storm's intensity (minimum sea level pressure and maximum winds), the warning contains forecasts of the positions and intensities of the system for the 12, 24, 36, 48, 60 and 72 hours ranges (starting from the synoptic time of the advisory). The Dvorak satellite analysis of the system is generally also included.

These Tropical Cyclone Forecast Warning bulletins are issued whenever a tropical or subtropical or extratropical (from tropical origin) cyclone is present on the SouthWest Indian Ocean every 6 hours, at 0000, 0600, 1200, 1800 UTC. For weak systems these advisories may be issued on an irregular framework.

Example

WTIO30 FMEE 130010
RSMC / TROPICAL CYCLONE CENTRE / LA REUNION
TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN)

0.A WARNING NUMBER : 10/12/20052006
1.A SEVERE TROPICAL STORM 12 (DUMMY)

2.A POSITION 2006/04/13 AT 0000 UTC :
WITHIN 20 NM RADIUS OF POINT 13.0S / 55.4E
(THIRTEEN DECIMAL ZERO DEGREES SOUTH AND FIFTY FIVE DECIMAL FOUR DEGREES EAST)
MOVEMENT : WEST-SOUTH-WEST 6 KT

3.A DVORAK ANALYSIS : 4.0/4.0 MINUS/D 1.5/24h
4.A CENTRAL PRESSURE : 980 HPA
5.A MAX AVERAGE WIND SPEED (10 MN) : 55 KT
RADIUS OF MAXIMUM WIND (RMW) : 20 KM

6.A EXTENSION OF WINDS BY QUADRANTS (KM):
30 KT NE: 200 SE: 400 SO: 400 NO: 200
50 KT NE: 030 SE: 030 SO: 030 NO: 030

7.A FIRST CLOSED ISOBAR (PRESSURE / AVERAGE DIAM): 1006 HPA / 800 KM
8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: DEEP

1.B FORECASTS:
12H: 2007/03/13 12 UTC: 13.1S/54.5E, MAX WIND=060KT, SEVERE TROP. STORM.
24H: 2007/03/14 00 UTC: 13.6S/53.6E, MAX WIND=060KT, SEVERE TROP. STORM.
36H: 2007/03/14 12 UTC: 14.6S/52.8E, MAX WIND=070KT, TROPICAL CYCLONE.
48H: 2007/03/15 00 UTC: 15.2S/52.0E, MAX WIND=075KT, TROPICAL CYCLONE.
60H: 2007/03/15 12 UTC: 15.5S/51.7E, MAX WIND=080KT, TROPICAL CYCLONE.
72H: 2007/03/16 00 UTC: 15.8S/51.4E, MAX WIND=085KT, TROPICAL CYCLONE.

2.B OTHER INFORMATION:
T=CI=4.0-.
THE SYSTEM KEEPS ON REGULARLY INTENSIFYING AND SHOWS A CDO PATTERN ON THE LAST MET7 VISIBLE IMAGERY,
BUT A BUILDING EYE IS VISIBLE ON THE LAST MICROWAVE DATA. DUMY SHOULD BENEFICIATE OF GOOD ENVIRONMENTAL
CONDITIONS FOR THE NEXT 48 HOURS AND GRADUALLY INTENSIFY BUT AT A BELOW CLIMATOLOGICAL RATE.
THE SYSTEM IS EXPECTED TO KEEP ON TRACKING GLOBALLY WESTWARDS ON THE NORTHERN EDGE OF THE HIGH PRESSURES
FOR THE NEXT 12 HOURS AND THEN TO CURVE SOUTHWESTWARDS TOWARDS A TROUGH TRANSITING IN THE SOUTH.

How to read

The analysis and forecast warning advisory is generally composed of several easily identified sections. These sections if present in the advisory will always occur in the order specified here. Click on each section title to read the brief description of the section contents in the bulletin’s example shown for tropical cyclone DUMMY.

1. Identification
2. Position and motion
3. Dvorak Analysis
4. Minimum central pressure
5. Max average wind
6. Winds extension
7. First closed isobar (pressure/average diameter)
8. Vertical extension of cyclone circulation
9. Forecasts
10.Other information


WTIO30 FMEE 130010
RSMC / TROPICAL CYCLONE CENTRE / LA REUNION
TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN)

0.A WARNING NUMBER : 10/12/20052006
1.A SEVERE TROPICAL STORM 12 (DUMMY)

Section: Identification (of the advisory, of the issuing centre and of the system)

This section contains the assigned World Meteorology Organization (WMO) document identifier (WTIO30), the WMO issuing centre header (FMEE), the issuing date and time for the warning (here 13th at 00h10 UTC), identification of the issuing centre (in this case RSMC/Tropical cyclone centre/La Reunion), and the type of the advisory (here Tropical Cyclone Analysis and Forecast bulletin).
Then comes the warning number in section 0.A. The first digits refer to the warning number and are followed by the ranking number of the system within the referred cyclone season (in this case, it is the warning number 10 related to the system number 12 of the cyclone season 2005-2006).
Part 1.A indicates the storm type (area of disturbed weather, tropical disturbance, tropical depression, moderate tropical storm, severe tropical storm, tropical cyclone, intense tropical cyclone, very intense tropical cyclone, subtropical depression, etc...), the storm number and name in brackets (if existing - systems are normally named once they become moderate tropical storm).

2.A POSITION 2006/04/13 AT 0000 UTC :
WITHIN 20 NM RADIUS OF POINT 13.0S / 55.4E
(THIRTEEN DECIMAL ZERO DEGREES SOUTH AND FIFTY FIVE DECIMAL FOUR DEGREES EAST)
MOVEMENT : WEST-SOUTH-WEST 6 KT

 Section: Position and Motion

This section provides the location of the system's centre in latitude and longitude (in degree and tenth of degree) with the date/time of validity (YYYY/MM/DD). Before comes an indication about the uncertainty of the position in nautical miles (optional). Then follows the current motion of the system in knots or nautical miles per hour (1kt = 1nm = 1.852 km/h), with the direction expressed in terms of 16 compass directions (north, north-northeast, east-northeast, east...)

3.A DVORAK ANALYSIS : 4.0/4.0 MINUS/D 1.5/24h

Section: Dvorak analysis

This section details the Dvorak intensity analysis as followed: T/Ci, trend, past T tendency.
T is the Dvorak number and Ci the current intensity. The T trend can be ”PLUS” or ”MINUS” or left blank if no change is expected. The past tendency can be ”D” for ”Developing”, ”W” for ”Weakening”, ”S” for ”Stationary”.
In this example, T=Ci=4.0, the system is developing, and has ”won” 1.5 T in 24 hours on the Dvorak scale. The ”MINUS” trend indicates the current or forecast tendency evolution changes: in this case intensification rate should be slower for the next 24 hours than the 1.5 T increase previously observed.
4.A CENTRAL PRESSURE : 980 HPA

Section : Minimum central pressure

This section gives the minimum sea level central pressure of the storm in hPa.

5.A MAX AVERAGE WIND SPEED (10 MN) : 55 KT
RADIUS OF MAXIMUM WIND (RMW) : 20 KM

 Section: Max average wind speed

This section indicates the maximum 10-minute average wind speed, in knots (1 knot = 1 nautical mile per hour = 1852 m per hour) and the value in km of the radius of maximum wind (distance from the centre where blow these winds).

6.A EXTENSION OF WINDS BY QUADRANTS (KM):
30 KT NE: 200 SE: 400 SO: 400 NO: 200
50 KT NE: 030 SE: 030 SO: 030 NO: 030

Section: Extent of winds by thresholds and by geographical quadrants

This section indicates the wind radii (in km) from the system's centre for different wind thresholds. If present these quadrant values are provided for two wind thresholds : near gale force winds (30 kt) and storm force winds (50 kt).
In this example, near gale force winds exist up to 200 km in the northeastern quadrant, up to 400 km in the southeastern quadrant, up to 400 km in the southwestern quadrant, and up to 200 km in the northwestern quadrant, of the estimated storm's centre. Storm force winds exist within 30 km radius of the centre.
If no strong winds exist, this section will indicate: NIL.

7.A FIRST CLOSED ISOBAR (PRESSURE / AVERAGE DIAM): 1006 HPA / 800 KM

Section: first closed isobar

This section provides the pressure value (in hPa) and the diameter (in km) of the first (outermost) closed isobar around the system. This section is assessed thanks to the available observations, if possible. This information is mainly provided for the numerical weather products.

8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: DEEP

Section: Vertical extension of cyclone circulation

This information about vertical extension of the cyclone circulation can take three different values: deep, medium and shallow, depending on the estimated vertical extent of the cyclonic circulation within the atmospheric column.

1.B FORECASTS:
12H: 2006/04/13 12 UTC: 13.1S/54.5E, MAX WIND=060KT, SEVERE TROP. STORM.
24H: 2006/04/14 00 UTC: 13.6S/53.6E, MAX WIND=060KT, SEVERE TROP. STORM.
36H: 2006/04/14 12 UTC: 14.6S/52.8E, MAX WIND=070KT, TROPICAL CYCLONE.
48H: 2006/04/15 00 UTC: 15.2S/52.0E, MAX WIND=075KT, TROPICAL CYCLONE.
60H: 2006/04/15 12 UTC: 15.5S/51.7E, MAX WIND=080KT, TROPICAL CYCLONE.
72H: 2006/04/16 00 UTC: 15.8S/51.4E, MAX WIND=085KT, TROPICAL CYCLONE.

Section: Forecasts

This section gives the 12, 24, 36, 48, 60, 72-hour forecast for the tropical cyclone's position and associated maximum 10-min average wind (in knots) with corresponding storm type.

2.B OTHER INFORMATION:
T=CI=4.0-.
THE SYSTEM KEEPS ON REGULARLY INTENSIFYING AND SHOWS A CDO PATTERN ON THE LAST MET7 VISIBLE IMAGERY, BUT A BUILDING EYE IS VISIBLE ON THE LAST MICROWAVE DATA. DUMY SHOULD BENEFICIATE OF GOOD ENVIRONMENTAL CONDITIONS FOR THE NEXT 48 HOURS AND GRADUALLY INTENSIFY BUT AT A BELOW CLIMATOLOGICAL RATE. THE SYSTEM IS EXPECTED TO KEEP ON TRACKING GLOBALLY WESTWARDS ON THE NORTHERN EDGE OF THE HIGH PRESSURES FOR THE NEXT 12 HOURS AND THEN TO CURVE SOUTHWESTWARDS TOWARDS A TROUGH TRANSITING IN THE SOUTH.

 Section: Other information

This part gives any additional information useful to enlighten data provided within the bulletin’s body.




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