Frequently Asked Questions
- The Long-Range Tropical Cyclone Outlook for Australia (TCO-AU) generates freely-available deterministic and probabilistic tropical cyclone (TC) count outlooks for Australia and its regions.
- Updates are provided monthly (July-January) so that TCO-AU can consider the latest changes in ocean temperatures and atmospheric variability. Pre-season and In-season outlooks are derived:
- Pre-season outlooks are generated every month between July and October and provide guidance for the November-April tropical cyclone season. Pre-season outlooks offer up to four months lead time before the official start of the Australian TC season.
- In-season outlooks are generated monthly between November and January (see table below).
- As TCO-AU is a new outlook product, the first outlook for the 2020/21 Australian TC season was released in September. For the 2021/22 Australian TC season, the first extended-range guidance will be released in July 2021.
|Pre-season Outlook||July, August, September, October||November-April|
- Australian Region (AR): 5°-40°S, 90°-160°E
- Eastern Region (AR-E): 5°-40°S, 142.5°-160°E
- Northern Region (AR-N): 5°-40°S, 125°-142.5°E
- NW Region (AR-NW): 5°-40°S, 105°-130°E
- Western Region (AR-W): 5°-40°S, 90°-125°E
- TCO-AU uses multivariate Poisson regression to derive its TC count predictions. Models are trained on historical relationships between seasonal TC frequency and ocean-atmosphere variability from 1970-present.
- Historical best-track TC data is used from the Australian Best-Track Tropical Cyclone Database. This dataset contains historical best-tracks for TC events south of the equator between 90°E and 160°E from 1906 to present. This database is maintained by the Australian Bureau of Meteorology and can be accessed here.
- Models consider a total of 14 indices representing coupled ocean-atmosphere variability (figure below) including El Niño-Southern Oscillation, the Southern Annular Mode, and Indian Ocean sea surface temperature variability.
- Before generating an outlook, 10 unique predictor models are tested per location. The model with the highest skill based on the training period is chosen to derive the next outlook.
- See Magee and Kiem (2020) for more information.
Pre-season TCO-AU outlooks will be generated every month between July and October, while in-season outlooks will be generated between November and January. As TCO-AU is a new outlook product, the first outlook for the 2020/21 Australian TC season was released in September. For the 2021/22 Australian TC season, the first extended-range guidance will be released in July 2021.
|September TC Outlook||23rd September 2020|
|October TC Outlook||21st October 2020|
|In-season Outlook||November TC Outlook||18th November 2020|
|December TC Outlook||23rd December 2020|
|January TC Outlook||20th January 2021|
- Diamond and Renwick (2015) found that a synergy between SAM and ENSO shows an increased number of Southwest Pacific TCs undergo ex-tropical transition reaching further south during positive SAM and La Niña conditions, which may have implications for the east coast of the AR, where exposure is high. Magee et al. (2020) demonstrated that SAM was an important contributor for improved TC outlooks in the SWP. SAM has previously been shown to be associated with seasonal hydroclimatic variability across Australia (Hendon et al. 2007; Gillett et al. 2006; Risbey et al. 2009; Kiem and Verdon-Kidd 2009; Gallant et al. 2012), which suggests SAM should also be considered for inclusion in TC prediction schemes for the AR.
- Indian Ocean sea surface temperature variability has been shown to drive changes on where TCs form in the Australian and Southwest Pacific region. For Australia, Wijnands et al. (2015) found that the Dipole Mode Index (DMI) was the most frequently used index used in support vector regression models, when considered amongst a host of other indices, including eight ENSO indices. This is also consistent with Magee et al. (2020) where indices representing Indian Ocean SST variability were frequently selected for predicting TC counts for island and regional-scale TC outlooks across the SWP region.
- Models perform well in capturing the variability of TC frequency for monthly pre-season (July-October) and in-season (November-January) outlooks.
- Magee and Kiem (2020) comprehensively evaluate model performance for each location.
TCO-AU is a statistically-driven TC outlook for Australia. Rolling monthly updates will be provided between July and January so predictive models used in TCO-AU can consider the latest changes in ocean temperature and atmospheric variability. The following details should be considered when using TCO-AU:
- Guidance from TCO-AU does not and should not replace the advice provided by the Australian Bureau of Meteorology.
- TCO-AU provides guidance for the tropical cyclone season only (November-April), and does not consider tropical cyclones outside of these months.
- Timescales associated with outlooks (months) are different to shorter-term weather forecasts (hours to days). In the case of outlooks, particularly long-range outlooks such as those presented here, TCO-AU provides guidance up to four months before the start of the Australian TC season. As such, it is possible for daily or weekly changes in predictors (i.e. ocean temperatures and atmospheric variability) to influence TC numbers and result in discrepancies with the long-range TC outlooks.
- Monthly TCO-AU guidance will track any changes in ocean temperature/atmosphere variability, which may result in changes in guidance from one outlook to another. Subscribing to TCO-AU is the best way for end-users to stay up to date with the latest TCO-AU updates.
- Users should evaluate model skill and model consensus contained within the guidance document to inform decision-making.
- TCO-AU is an experimental platform and should ideally be used in combination with other guidance for decision-making. TCO-AU does not accept any liability associated with decisions that are made using this guidance.
- It does not take a landfalling TC to cause significant and life-threatening impacts. Always be alert. Listen to the advice of the Australian Bureau of Meteorology and relevant state government authorities.