FINOLIAN METEOROLOGICAL CENTRE TROPICAL CYCLONE …

Subtropical Storm Aurora 2-4 March 2021

Subtropical Storm Aurora 1

FINOLIAN METEOROLOGICAL CENTRE TROPICAL CYCLONE REPORT

SUBTROPICAL STORM AURORA (AU012021)

2-4 March 2021

Alex Avery H.

Finolian Meteorological Centre 4 March 2021

VISIBLE SATELLITE IMAGERY OF SUBTROPICAL STORM ‘AURORA’ AT PEAK INTENSITY AT 1045 UTC 2 MARCH 2021



SYNOPTIC HISTORY Aurora began as a large, broad extratropical storm over the northern Eastern Ocean on 26 February. Several smaller vortices developed within the low, as it continued generally southeastward. At 0900 AST/FOST, on 29 February, the Nxsa Hurricane Agency began monitoring the cyclone for potential subtropical development. Forecaster Garcia of the NHA gave the system a slim but possible change of subtropical transition, stating “An extratropical cyclone far north in the Eastern Ocean is being monitored for possible subtropical development. The low, marked as Invest 90L, is not expected to develop significantly as it moves south-east.” Later that day, the Finolian Meteorological Centre began to monitor the system as well. On 1 March, the Finolian Meteorological Centre gave the system a 50/50 chance of developing. However, later that day, the NHA overwrote their prediction, and estimated that the system was unlikely to make a subtropical transition. The system, dubbed “Invest 90O”, defied all predictions and became a subtropical storm at 1000 EST/ZST, according to forecaster Alex of the FMC. After its subtropical transition, Aurora continued southeastward. While cruising in around the storm, FS Anojtuu recorded sustained winds upwards of 26 knots, and gusts of 32 knots, when it entered the outer areas of the system. The wind field began to shrink and contract, denoting its disconnection from the front it was originally attached to. The FMC noted the system’s small size, as the wind field extended roughly 30 nautical miles from the centre. Once again, forecaster Alex of the FMC stated “Aurora has an unusually small size for a system of this latitude. However, given its subtropical characteristics, this isn’t completely unseen in other similar systems.” At 1700 EST/ZST, Aurora reached its peak intensity of 50 miles per hour and 997 millibars. Aurora weakened slightly, before making an eastward turn. It weakened, as an upper-level low began to increase its forward speed to the east. At 0800 EST/ZST, Aurora unexpectedly strengthened, reaching a secondary peak intensity of 45 miles per hour. Shortly after this, however, Aurora’s convection began to decrease, and was declared a subtropical depression at 1700 EST/ZST. The FMC issued its final advisory on the system at 2300 EST/ZST as it became a remnant low, devoid of convection. The Finolian Meteorological Centre declared the system a remnant low, although kept tracking its remnant as they brought somewhat hazardous conditions to Finolian overseas territories.



METEOROLOGICAL STATISTICS All observations in Aurora (figures 2 and 3) are based off of satellite-derived data and estimations.

Winds and Pressure The ship FS Anojtuu reported winds of 32 knots about 30 nautical miles from the center of the storm, on 4 March, around 0300 EST/ZST. At the time, the system had 45 mile per hour winds and a pressure of 998 millibars. Aurora’s estimated peak is based off of buoy observations, as well as satellite-derived information. A Finolian buoy, located at 56.192N, 16.938E observed winds of 47 miles per hour as the center of Aurora passed over it, near peak intensity. The 998 millibar estimated minimum pressure is based off of several satellite estimates.

Rainfall and Flooding There were no reports of flooding, as Aurora had no direct impact to land.

CASUALTY AND DAMAGE STATISTICS Aurora reportedly caused one fatality after a personal sailboat capsized near the outer bands of the storm. The boat was occupied by three individuals, who were apparently not using the right precautions while sailing. Elsewhere, there were no other reports of casualty associated with Subtropical Storm Aurora.

FORECAST AND WARNING CRITIQUE The formation and development of Aurora was originally poorly forecast by both the FMC and NHA. The first advisory, issued by the NHA, gave the system a 10% chance of developing in 5 days. On 1 March, the FMC gave the system a 50% chance of development, and then the NHA continued to decrease its chances of formation, despite continued development. Later, however, the invest became a subtropical storm as issued by the FMC.



Several advisories were initiated by the FMC and NHA during Aurora’s lifespan. Each centre took turns issuing advisories, and used estimates from mostly satellite-derived information. No tropical storm watches or warnings were issued, however storm surge warnings were issued for areas several hundred miles from the storm.



Table 1. Best track for Subtropical Storm Aurora, 2-4 March 2021.

Date/Time (UTC) Pressure (mb) Wind Speed (mph) Stage

26/0500 1000 35 extratropical

26/1100 1000 35 "

26/1700 998 35 “

26/2300 999 40 “

27/0500 999 45 “

27/1100 998 45 “

27/1700 997 45 “

27/2300 996 45 "

28/0500 996 45 “

28/1100 994 50 “

28/1700 995 50 “

28/2300 995 45 “

01/0500 997 40 “

01/1100 999 35 “

01/1700 999 35 “

01/2300 999 40 “

02/0500 999 40 “

02/1100 998 45 subtropical storm

02/1700 997 50 “

02/2300 998 45 “

03/0500 998 45 “

03/1100 998 45 “



Date/Time (UTC) Pressure (mb) Wind Speed (mph) Stage

03/1700 999 40 “

03/2300 999 40 “

04/0500 998 45 “

04/1100 999 40 “

04/1700 1001 35 subtropical depression

04/2300 1003 35 remnant low

05/0500 1005 30 dissipated



Table 3. Number of hours in advance of formation associated with the first FMC or NHA Tropical Weather Outlook forecast in the indicated likelihood category. Note that the timings for the “Low” category do not include forecasts of a 0% chance of genesis

Hours Before Genesis

48-Hour Outlook 120-Hour Outlook

Low (<40%) 48 120

Medium (40-60%) 48 48

High (>60%) - -



Figure 1. Best track positions for Subtropical Storm Aurora, 2-4 March 2020.



Figure 2. Wind observations and best track wind speed curve Subtropical Storm Aurora, 2-4 March 2021.

Subtropical Storm Aurora, 2-4 March 2021



Figure 3. Observations of best track minimum central pressure for Subtropical Storm Aurora, 2-4 March 2021.

Subtropical Storm Aurora, 2-4 March 2021



Figure 4. Aurora, several minutes after being designated as a subtropical storm.



For further information, visit https://hypotheticalhurricanes.fandom.com/wiki/2021_Eastern_Ocean_hurricane_season

Written by Alex Avery H. - Finolian Meteorological Centre - Charlotte, North Carolina/Zborbya, Finolia

https://hypotheticalhurricanes.fandom.com/wiki/2021_Eastern_Ocean_hurricane_season

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