USE OF DVORAK TECHNIQUE IN JAKARTA TCWC

COUNTRY REPORT
SUBMITTED BY INDONESIAN DELEGATE FOR IWSATC 2011

  1. JAKARTA TCWC

Since 24th March 2008 Indonesia Meteorological Climatological and Geophysical Agency (BMKG) has been operating a Tropical Cyclone Warning Center in Jakarta (Jakarta TCWC). With reference to the WMO Tropical Cyclone Operational Plan for South Pacific and Southeast Indian Ocean (TCP 24), the Jakarta TCWC has responsibility to issue Tropical Cyclone Warning for area bounded by EQ 090ºE, 10S 090ºE, 10S 120ºE, 11S 120ºE, 11S 128ºE, 09S 128ºE, 09S 141ºE, EQ 141ºE.

Image 1: Jakarta TCWC Area of Responsibility (dark shadow)

  1. Operational Procedures / Guidance used in Jakarta TCWC

-Operational directive and forecaster duty list, adopted from Australian TCWC, developed and adjusted to conform with Jakarta TCWClocal conditions

-Cyclogenesis checksheet, as the principal tool for cyclogenesis analysis

-CI-pressure-wind relations conversion table

-Technical Bulletin provided by Australia TCWC

  1. Analysis and Forecasting Tools

There are 2 main tools in the Jakarta TCWC operational activities:

-TC Module, used for the product preparation and dissemination of tropical cyclone information

-Synergie, a beneficial integrated system of synoptic and upper air observation data, satellite imagery, and NWP model data which completed with a special cyclone module that is considered as Jakarta TCWC backupsystem.

Operational Design of Jakarta TCWC

  1. USE OF DVORAK TECHNIQUE IN JAKARTA TCWC
  1. Local Variation to Dvorak Technique

Jakarta TCWC Area of Responsibility is located very near to equator that tropical disturbance occurred is mostly at the early stage development with disorganized cloud pattern. When the disturbance develops into tropical cyclone, it formed a relatively small-sized storm with relatively short lifetime (Cyclone Kirrily in 2009, Cyclone Anggrek in 2010).

  1. Variation of Dvorak Technique Implementation between Forecasters

There are differences in the forecaster’s approach due to irregular cloud pattern which commonly encountered in the early stage development.Differences in analysis result have become a necessity. This is especially occurred in determining the coordinates of the circulation center. Using microwave imagery, circulation centre issue is never arising. Though unavailability of this data may causes coordinates difference up to one degree.

  1. Analysis Procedures Changes

During 3 years operational period of Jakarta TCWC, there has been no significant change in the operational procedure, especially related to the implementationof Dvorak method.

  1. Final Intensity versus CI

So far, determination of final intensity always matches the CI.

  1. Technology Advancement Influence Through Dvorak Technique

-Microwave imagery obtained from NRL Tropics Sitewebsite is very helpful in determining the circulation centerin many pre-cyclone cases.

-Scatterometer wind from ASCAT is used to compare with maximum wind.

-Various products from RAMMB CIRA particularly satellite surface wind analysis, is also used as consideration. Though we are not use the Digital Dvoraksince the value is often over estimated.

  1. Ancillary Data

-Microwave imagery.

-Scatterometer wind.

-Satellite surface wind analysis.

  1. CI – Pressure – Wind Relation Used

Jakarta TCWC used Dvorak Conversion Table for Perth TCWC as initial guidance. But during the operational period, it is noted that the central pressure of tropical cyclones occurred in Jakarta TCWC AoR is tend to be bigger than pressure listed in the table. It is noted that the difference is ranging from 2 to 19 mb depends on the cyclone intensity.This was suspected due to they are located very close to the equator ( <10 degrees south).

Comparison between central pressure of tropical cyclones occurred in the Jakarta TCWC Area of Responsibility (red) and central pressure in the Dvorak Conversion Table for Perth TCWC (purple).

Difference between central pressure of tropical cyclones occurred in the Jakarta TCWC Area of Responsibility and central pressure in the Dvorak Conversion Table for Perth TCWC.

  1. Best Track Records

No best track record has been produced by TCWC Jakarta so far.