T1803 JELAWATRSMC Tokyo – Typhoon Center
Japan Meteorological Agency

Track & Intensity of JELAWAT- JELAWAT formed east of Palau late March 2018
- Initially moved WNW and gradually turned north- Made a nearly right-angle sudden turn eastward- Reached 105kt, Dvorak CI=7.0 at peak
31

Best track intensity changes

2928
2726
Mar 25Max. sustained wind30

Rapidintensification

Peaked at 105kt& Dvorak CI=7.0
at 06UTC Mar 30

HIMAWARI-8 IR images

Philippine Sea

Genesis of JELAWAT- Climatologically, average TC genesis frequency in March is 0.3.
- Genesis of JELAWAT was associated with an equatorial Rossby wave structure
seen during the preceding days
- This Rossby wave structure led to wetter than normal mid-level atmosphere.
Stream function and wind vectors at850hPa averaged for Mar. 21 to 25 2018

Specific humidity anomalies at 600hPa
averaged for Mar. 21 to 25 2018

Equatorial symmetric
cyclonic structure

Wetter than normal
mid-level atmosphere

DryWetBest track & track forecast for JELAWAT
Initial: 12UTC Mar. 26, 20183130

- No NWP model was able
to predict the sudden
eastward turn- Discrepancy in latitude
between forecast andactual track is over 4o29282726

Mar. 25

Best track
JMA official
GSM
ECMWFUKMETNCEPWhy was JELAWAT’s early track forecast so poor?
- In GSM forecast starting at 12UTC Mar 26, a slightly stronger ridge
was predicted to the east of JELAWAT than the analysis- This ridge might have prompted JELAWAT to head northward inNWP model
GPH at 500hPa for 12UTC Mar 29
JRA55

GPH at 500hPa for 12UTC Mar 29(initial: 12UTC Mar 26)
GSM Forecast

Best track & intensity forecast for JELAWAT- Rapidly intensified by 35kt in 24 hours from 06UTC Mar. 26 and peaked at 105kt.
- TIFS failed to predict this RI but predicted a conventional intensification instead.
- JMA Official forecast was further conservative, because adjusted down toward
GSM.

Intensity changes (Best track & forecast)

Intensity(kt)Peak intensity
at 105kt
Intensified by35kt in 24hrs

TIFS initial time:
12UTC Mar. 26
Best track
TIFS guidance
GSM
Official forecast

Sudden eastward
turn here

Forecast time

TIFS (intensity forecast guidance)---JMA forecasters primarily depend onExplanatory factors for TIFS
Typhoon Intensity Forecast Scheme based(not exhaustive)
on SHIPS (TIFS) for forecast guidance
Variable
Description
name
TIFS predicts intensity changes exploiting
PERSISTENCE Change in max sustained wind during the last
statistical relationship btw TC intensity
12 hourschanges and environmental conditions.
SHEAR
Vertical wind shear between 200 and 850hPa
levelsTIFS originates from SHIPS, adapted for thebetween the latest TC intensity andwestern North Pacific. (Many thanks to Dr. POTENTIAL Difference
its maximum potential intensityDeMaria)
TANGENTIAL Tangential wind speed around the TC at850hPa level

FT=120FT=18
FT=12
FT=6 FT=0

Atmosphere & ocean
conditions averaged over thevicinity of a typhoon forevery 6-hr step

MAXWIND

The latest max sustained wind

TEMP200,
TEMP250

Temperature at 200 and 250hPa

MID_RH

Relative humidity in the mid-troposphere

VOR850Vorticity at 850hPa

DIV200

Divergent at 200hPa

MOTION

Zonal component of translation speed of theTC

OHC

Ocean heat contentIRPortion of cloud area with infrared irradiancebelow -30oC

Atmospheric conditions- The subtropical jet stream flowed around the latitudes of 25-35 degrees north.
- Vertical wind shear (VWS) was to increase along the forecast track- VWS was weak to moderate along the actual track

Wind vector and zonal wind at 200hPa
for 12UTC Mar. 29, 2018

Forecast track
Actual trackOcean conditions-SSTs were unfavorable for intensification at 24-26oC along the forecast track
SSTs were more favorable at above 27oC along the actual track
Same can be said about TCHP
This discrepancy might have partly caused the poor intensity forecast
Sea surface temperaturesTropical cyclone heat potential
for Mar. 27, 2018
for Mar. 27, 2018

Forecast track

Forecast track
Actual track

Actual trackSummary- JELAWAT formed late March from an equatorial Rossby
wave structure- Track forecasts at early stages were poor. No NWP
model was able to predict JELAWAT’s sudden turn- Intensity forecasts at early stages were poor as well, atleast partly attributable to track forecast error- Acknowledge track forecasts have come a long way
thanks to NWP model improvement- But NWP models could sometimes miserably fail.
- Encourage NWP modelers & researchers to investigate“bust cases” of track forecast like JELAWAT.