“Tropical Cyclone Formation Alert”的意思、由来-开放百科全书

词条 Tropical Cyclone Formation Alert

释义

Parts of the TCFA
Section 1 Section 2 Section 3 Sample alert
Issuance checklist
Surface 500 mb height 200 mb height Sea surface temperature Satellite data Miscellaneous
See also
References
External links

A Tropical Cyclone Formation Alert (TCFA) is a bulletin released by the U.S. Navy-operated Joint Typhoon Warning Center in Honolulu, Hawaii or the Fleet Weather Center in Norfolk, Virginia, warning of the possibility of a tropical cyclone forming from a tropical disturbance that has been monitored. Such alerts are generally always issued when it is fairly certain that a tropical cyclone will form and are not always released prior to cyclone genesis, particularly if the cyclone appears suddenly. The TCFA consists of several different checks that are performed by the on-duty meteorologist of the system and its surroundings. If the condition being checked is met, a certain number of points are given to the system.

Parts of the TCFA

Section 1

The first section of the TCFA contains information on the area of the alert as well as the estimated center of the circulation. The estimated maximum sustained winds are provided as well.

Section 2

The second section generally contains more specific information pertaining to the system. Information such as location relative to nearby cities or places of interest can usually be found in this section. Some of the reasoning for the issuance of the TCFA, which usually consists of recent changes in the system, can be found here. The section always ends with a statement as to the potential for development, which the JTWC will rank as either low, medium, or high (formerly poor, fair, or good).

Section 3

This final section contains the time of the next bulletin on this system, which will update the system's progress over the elapsed time. The bulletin will be either another TCFA, a cancellation message, or the first advisory/warning on the system. The issuance of another TCFA would occur if the system remains in a state similar to its current state. A cancellation message would indicate that the likelihood of the system to develop into a tropical cyclone at the current time has decreased. An advisory would indicate that a tropical cyclone has indeed formed, and poses a future threat to the areas in the box defined in Section 1.

Sample alert

WTPN22 PGTW 031030 MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC// SUBJ/TROPICAL CYCLONE FORMATION ALERT 031021Z JUL 06// RMKS 1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN 100 NM EITHER SIDE OF A LINE FROM 16.4N 110.2E TO 19.7N 109.2E WITHIN THE NEXT 12 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME. WINDS IN THE AREA ARE ESTIMATED TO BE 20 TO 25 KNOTS. METSAT IMAGERY AT 030900Z INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 16.7N 110.1E. THE SYSTEM IS MOVING NORTH-NORTHWESTWARD AT 07 KNOTS. 2. REMARKS: THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 16.3N 110.2E, IS NOW LOCATED NEAR 16.7N 110.1E, APPROXIMATELY 130 NM SOUTH- SOUTHEAST OF HAINAN, CHINA. RECENT ANIMATED INFRARED IMAGERY SHOWS CONVECTION HAS CONTINUED TO BECOME MORE CONSOLIDATED AND THERE IS NOW NORTHERLY RETURN FLOW IN THE NORTHWESTERN QUADRANT OF SYSTEM. UPPER LEVEL ANALYSIS INDICATES FAVORABLE EQUATORWARD OUTFLOW AND MODERATE VERTICAL WIND SHEAR. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 20 TO 25 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1003 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS UPGRADED TO HIGH. 3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED

BY 041030Z.//

Issuance checklist

The JTWC and [https://metoc.ndbc.noaa.gov/ProductFeeds-portlet/img/fwc-n/ FWC-N] follow a checklist when deciding whether or not to issue a TCFA on tropical disturbances. The checklist is updated every few years, and the JTWC checklist may differ slightly from the FWC-N checklist, which is shown below. If a system gets 35 to 38 points, a TCFA may be issued depending on Dvorak trends, and if a system gets 39 points or more a TCFA should be issued.

Surface

Condition	Points
A circulation is evident using visible satellite, shortwave infrared, microwave imagery or QuikSCAT/Windsat ambiguities	3 points
A circulation has been evident for at least 24 hours	5 points
A westerly surface- or gradient-level wind of 5 kn that is within 200 nmi (370 km, 230 mi) south of the centre of the disturbance	5 points
Any wind associated with the system is at least 20 kn	2 points
Any wind associated with the system is at least 25 kn	3 points
Any wind associated with the system is at least 30 kn	4 points
A weather station within 200 nm of the system has reported had a pressure drop of 2 mb over 24 hours	3 points
A weather station within 200 nmi of the system has had a pressure drop of 3 mb over 24 hours	4 points
The estimated MSLP of the system is less than 1010 to 1009 mb	3 points
The estimated MSLP of the system is 1008 mb or less	4 points

500 mb height

Condition	Points
There is evidence of at least an inverted trough	2 points
There is evidence of a closed circulation in the system	4 points

200 mb height

Condition	Points
Westerly flow of at least 15 kn over the disturbance	-4 points
There is evidence of anticyclonic outflow over the centre of the disturbance	4 points
Easterly flow of at most 20 kt over the disturbance	3 points

Sea surface temperature

Condition	Points
The sea surface temperature is 26 Celsius (78.8 Fahrenheit) or higher	3 points

Satellite data

Condition	Points
The system has persisted for at least 24 hours	3 points
The system has persisted for at least 48 hours	4 points
The system has persisted for at least 72 hours	5 points
The system has a Dvorak classification of T1.0 to T1.5 from all three agencies (TAFB, SAB, AFWA)	3 points
The system has a Dvorak classification of T1.5 to T2.0 from all three agencies	5 points
The Dvorak final-T number has decreased by T0.5 to T1.0 from two or more agencies	-2 points

Miscellaneous

Condition	Points
The cloud system is at least 5 degrees latitude away from the equator	3 points
The tropical system is within 72 hours of reaching a Department of Defense resource	3 points
The cloud system center and the satellite centre fixes for the system are within 2 degrees of each other	2 points

References

[https://metoc.ndbc.noaa.gov/ProductFeeds-portlet/img/fwc-n/html/warnings.jsp?page=warnings_tropical.jsp Fleet Weather Center Norfolk Tropical Page]

External links

JTWC Advisories Page

1 : Tropical cyclone meteorology

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