EPAC: HILDA - Post-Tropical

[Yellow Evan]

* GFS version *
* EAST PACIFIC 2021 SHIPS INTENSITY FORECAST *
* IR SAT DATA AVAILABLE, OHC AVAILABLE *
* INVEST EP902021 07/30/21 18 UTC *

TIME (HR) 0 6 12 18 24 36 48 60 72 84 96 108 120 132 144 156 168
V (KT) NO LAND 40 44 48 52 56 62 67 71 69 71 69 67 64 60 54 48 42
V (KT) LAND 40 44 48 52 56 62 67 71 69 71 69 67 64 60 54 48 42
V (KT) LGEM 40 44 47 50 52 54 57 61 62 62 60 59 56 52 45 39 34
Storm Type TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP

SHEAR (KT) 10 8 8 11 12 13 15 13 19 18 18 9 15 12 12 15 19
SHEAR ADJ (KT) 1 4 4 0 -1 -4 -5 -6 -3 -4 -2 0 -4 -6 -4 -4 -2
SHEAR DIR 332 1 40 58 68 67 63 49 42 46 38 43 17 30 359 327 334
SST (C) 28.3 28.5 28.8 28.7 27.7 26.9 27.5 27.2 26.4 26.4 26.7 26.3 25.7 25.2 24.9 24.7 24.3
POT. INT. (KT) 148 150 153 152 141 133 139 135 126 126 129 125 119 113 111 110 106
200 MB T (C) -52.6 -52.4 -52.8 -53.3 -53.3 -53.1 -53.2 -52.7 -52.9 -52.6 -52.8 -52.4 -53.0 -52.7 -53.1 -52.8 -53.0
200 MB VXT (C) 0.1 0.1 0.1 0.2 0.2 0.3 0.2 0.1 0.2 0.2 0.2 0.2 0.0 0.0 0.2 0.0 0.1
TH_E DEV (C) 4 4 3 3 3 2 2 2 2 2 2 3 3 2 2 2 2
700-500 MB RH 77 77 79 80 81 81 78 77 73 70 68 67 65 68 65 67 67
MODEL VTX (KT) 11 12 13 15 15 16 15 17 16 19 20 20 21 20 19 17 15
850 MB ENV VOR -9 -10 3 14 33 31 47 66 65 72 68 45 10 -11 -19 -13 -14
200 MB DIV 99 111 110 68 76 80 87 95 97 66 81 75 60 57 36 24 17
700-850 TADV -11 -8 -9 -9 -6 -4 -7 -10 -9 -10 -7 -5 -3 -2 -4 -5 -7
LAND (KM) 1195 1270 1289 1311 1344 1416 1520 1607 1662 1740 1835 1897 1927 1966 2020 2148 1973
LAT (DEG N) 11.9 xx.x xx.x xx.x xx.x xx.x xx.x xx.x xx.x xx.x xx.x xx.x xx.x xx.x xx.x xx.x xx.x
LONG(DEG W) 113.0 xxx.x xxx.x xxx.x xxx.x xxx.x xxx.x xxx.x xxx.x xxx.x xxx.x xxx.x xxx.x xxx.x xxx.x xxx.x xxx.x
STM SPEED (KT) 13 12 12 11 11 10 10 8 6 6 6 6 6 6 8 11 11
HEAT CONTENT 14 12 15 14 6 2 6 9 1 1 2 0 0 0 0 0 0

FORECAST TRACK FROM OFPI INITIAL HEADING/SPEED (DEG/KT):270/ 14 CX,CY: -13/ 0
T-12 MAX WIND: 30 PRESSURE OF STEERING LEVEL (MB): 477 (MEAN=587)
GOES IR BRIGHTNESS TEMP. STD DEV. 50-200 KM RAD: 19.0 (MEAN=14.5)
% GOES IR PIXELS WITH T < -20 C 50-200 KM RAD: 80.0 (MEAN=65.0)
PRELIM RI PROB (DV .GE. 35 KT IN 36 HR): 23.3

INDIVIDUAL CONTRIBUTIONS TO INTENSITY CHANGE
6 12 18 24 36 48 60 72 84 96 108 120 132 144 156 168
------------------------------------------------------------------------------
SAMPLE MEAN CHANGE 0. 0. 1. 1. 1. 2. 1. 1. 0. -0. -1. -2. -2. -3. -4. -4.
SST POTENTIAL 0. 1. 2. 3. 6. 9. 12. 15. 16. 17. 18. 17. 16. 14. 13. 12.
VERTICAL SHEAR MAG 0. 1. 1. 2. 2. 1. 1. -1. -2. -3. -3. -3. -2. -2. -3. -4.
VERTICAL SHEAR ADJ -0. -0. -1. -0. 0. 1. 2. 1. 1. 0. 0. 0. 0. 0. 1. 1.
VERTICAL SHEAR DIR -0. 0. 1. 2. 4. 6. 7. 8. 8. 8. 8. 7. 6. 4. 3. 3.
PERSISTENCE 2. 3. 3. 3. 3. 2. 2. 2. 2. 2. 2. 2. 2. 2. 2. 2.
200/250 MB TEMP. -0. -0. -0. -0. -1. -1. -2. -3. -3. -3. -3. -2. -2. -1. -1. -1.
THETA_E EXCESS -0. -1. -1. -2. -3. -5. -6. -7. -8. -9. -9. -9. -10. -10. -12. -13.
700-500 MB RH 0. 0. 0. 1. 1. 1. 1. 2. 2. 2. 2. 2. 2. 3. 3. 5.
MODEL VTX TENDENCY 0. 1. 2. 3. 3. 4. 7. 6. 11. 11. 11. 11. 9. 7. 5. 3.
850 MB ENV VORTICITY -0. -0. -0. -0. -0. 0. 0. -0. -0. -0. -0. -0. -0. -0. 0. 0.
200 MB DIVERGENCE 0. 1. 1. 1. 1. 2. 3. 5. 5. 5. 5. 4. 3. 1. -0. -1.
850-700 T ADVEC 0. 0. 0. 0. 0. -0. -0. -0. -0. -0. -0. -1. -1. -1. -2. -2.
ZONAL STORM MOTION 0. 0. 1. 1. 2. 3. 3. 3. 2. 2. 2. 2. 1. 1. 1. -0.
STEERING LEVEL PRES -0. -0. -1. -1. -1. -1. -2. -2. -2. -2. -2. -2. -2. -1. -1. -0.
DAYS FROM CLIM. PEAK 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. -0. -0.
GOES PREDICTORS 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0.
OCEAN HEAT CONTENT -0. -0. -0. -0. -0. -1. -1. -1. -0. -0. 0. 1. 1. 2. 3. 5.
RI POTENTIAL 0. 1. 2. 3. 4. 3. 2. 0. -0. -1. -1. -1. -1. -1. -1. -1.
------------------------------------------------------------------------------
TOTAL CHANGE 4. 8. 12. 16. 22. 27. 31. 29. 31. 29. 27. 24. 20. 14. 8. 2.

CURRENT MAX WIND (KT): 40. LAT, LON: 11.9 113.0

** 2021 E. Pacific RI INDEX EP902021 INVEST 07/30/21 18 UTC **
(SHIPS-RII PREDICTOR TABLE for 30 KT OR MORE MAXIMUM WIND INCREASE IN NEXT 24-h)

Predictor Value RI Predictor Range Scaled Value(0-1) % Contribution
POT = MPI-VMAX (KT) : 109.1 40.5 to 149.3 0.63 5.1
12 HR PERSISTENCE (KT) : 10.0 -22.0 to 44.0 0.48 4.5
D200 (10**7s-1) : 92.8 -33.0 to 159.5 0.65 4.9
850-200 MB SHEAR (KT) : 9.7 19.6 to 1.3 0.54 3.9
MAXIMUM WIND (KT) : 40.0 22.5 to 132.0 0.50 2.8
STD DEV OF IR BR TEMP : 19.0 37.8 to 2.1 0.53 2.7
BL DRY-AIR FLUX (W/M2) : 58.0 800.8 to -82.5 0.84 -4.8
HEAT CONTENT (KJ/CM2) : 12.2 2.7 to 106.7 0.09 0.4
%area of TPW <45 mm upshear : 0.0 56.6 to 0.0 1.00 1.6
2nd PC OF IR BR TEMP : -0.5 2.2 to -2.3 0.59 0.5

SHIPS Prob RI for 20kt/ 12hr RI threshold= 12% is 2.0 times climatological mean ( 6.3%)
SHIPS Prob RI for 25kt/ 24hr RI threshold= 25% is 2.0 times climatological mean (12.5%)
SHIPS Prob RI for 30kt/ 24hr RI threshold= 22% is 2.5 times climatological mean ( 8.6%)
SHIPS Prob RI for 35kt/ 24hr RI threshold= 21% is 3.3 times climatological mean ( 6.2%)
SHIPS Prob RI for 40kt/ 24hr RI threshold= 12% is 2.9 times climatological mean ( 4.2%)
SHIPS Prob RI for 45kt/ 36hr RI threshold= 19% is 2.8 times climatological mean ( 6.7%)
SHIPS Prob RI for 55kt/ 48hr RI threshold= 16% is 2.7 times climatological mean ( 5.9%)
SHIPS Prob RI for 65kt/ 72hr RI threshold= 12% is 2.6 times climatological mean ( 4.7%)

Matrix of RI probabilities
------------------------------------------------------------------------------
RI (kt / h) | 20/12 | 25/24 | 30/24 | 35/24 | 40/24 | 45/36 | 55/48 |65/72
------------------------------------------------------------------------------
SHIPS-RII: 12.3% 24.9% 21.6% 20.7% 12.0% 18.9% 16.1% 12.4%
Logistic: 7.7% 27.7% 14.6% 7.6% 1.6% 9.0% 17.0% 8.3%
Bayesian: 10.1% 4.9% 2.6% 0.7% 0.1% 0.3% 0.1% 0.1%
Consensus: 10.0% 19.2% 12.9% 9.7% 4.6% 9.4% 11.1% 6.9%
DTOPS: 5.0% 14.0% 8.0% 6.0% 5.0% 8.0% 15.0% 23.0%

## ANNULAR HURRICANE INDEX (AHI) EP902021 INVEST 07/30/21 18 UTC ##
## STORM NOT ANNULAR, SCREENING STEP FAILED, NPASS=4 NFAIL=3 ##
## AHI= 0 (AHI OF 100 IS BEST FIT TO ANN. STRUC., 1 IS MARGINAL, 0 IS NOT ANNULAR) #

[cycloneye]

Tropical Storm Hilda Discussion Number 1
NWS National Hurricane Center Miami FL EP082021
300 PM MDT Fri Jul 30 2021

A pair of ASCAT passes from a few hours ago indicated that the area
of low pressure located about 800 miles south-southwest of the
southern tip of the Baja California peninsula has strengthened, and
is producing 35-40 kt winds on its east side. In addition,
satellite images show a fairly persistent area of showers and
thunderstorms on the south side of the circulation and the center
appears to be fairly well defined in recent visible images. Based
on these data, advisories are now being initiated on Tropical Storm
Hilda and the initial intensity is estimated to be 40 kt.

Hilda is moving westward at about 14 kt and is embedded in the flow
on the south side of a sprawling subtropical ridge that extends from
the south-central U.S. westward across the subtropical eastern
Pacific. A general west-northwestward motion at about the same
forward speed is expected during the next day or two as the synoptic
pattern holds. After that time, a decrease in forward speed is
predicted due to a combination of the subtropical ridge weakening
and the interactions with the areas of low pressure to the east and
west of Hilda. The ECMWF is the slowest model at long range due to
it showing the most interaction with the low to Hildas east. The
NHC track forecast lies generally near the model consensus and
roughly between the GFS and ECMWF models.

Hilda appears to be in generally conducive conditions for
strengthening with SSTs currently around 28 C, abundant mid-level
moisture, and fairly low wind shear. Given that these conditions are
expected to persist for another couple of days, steady strengthening
is forecast during that time period and Hilda is predicted to become
a hurricane in 24 to 36 hours. Beyond a couple of days, however,
moderate easterly shear, progressively drier air, and decreasing
SSTs should end the strengthening trend and induce gradual weakening
of the cyclone. The NHC intensity forecast lies near the middle of
the guidance envelope, closest to the intensity model consensus
IVCN.


FORECAST POSITIONS AND MAX WINDS

INIT 30/2100Z 12.1N 113.6W 40 KT 45 MPH
12H 31/0600Z 12.6N 115.4W 50 KT 60 MPH
24H 31/1800Z 13.2N 117.6W 60 KT 70 MPH
36H 01/0600Z 13.8N 119.7W 70 KT 80 MPH
48H 01/1800Z 14.3N 121.6W 75 KT 85 MPH
60H 02/0600Z 14.9N 123.1W 75 KT 85 MPH
72H 02/1800Z 15.3N 124.4W 70 KT 80 MPH
96H 03/1800Z 16.6N 126.4W 65 KT 75 MPH
120H 04/1800Z 18.3N 129.5W 55 KT 65 MPH

$$
Forecaster Cangialosi

[Kingarabian]

The models have been all over the place with its track. Interesting to see how the NHC handles it. Maybe it can get enough separation from TD9 and future 91E to allow for a more WNW track for more ACE.

[ElectricStorm]

This will have a few days to do something before getting ripped apart. Maybe we'll see a decent hurricane out of this. Not expecting a major, but you never know...

[Kingarabian]

This will have a few days to do something before getting ripped apart. Maybe we'll see a decent hurricane out of this. Not expecting a major, but you never know...

Currently looks like it will be a beast. But the emergence of TD9 and future 91E could put a lid on it.

[Yellow Evan]

Given the current shear over it and disturbances to its east and west, am skeptical of serious intensification, especially beyond 48 hours. SSTs start to really drop off north of 15-16N.

[Kingarabian]

CMISS showing mid shear dropping below 10kts for both systems. Though mid shear has been super sneaky so far.

[Yellow Evan]

TXPZ29 KNES 302333
TCSENP
CCA

A. TROPICAL DISTURBANCE (90E)

B. 30/1730Z

C. 12.8N

D. 113.0W

E. FIVE/GOES-W

F. T2.0/2.0

G. IR/EIR/VIS/GMI

H. REMARKS...CORRECTED FOR VALUE AND BASIS OF THE FT. 2/10 WHITE
BANDING AROUND THE LLCC MAKES THE DT EQUAL TO 1.5 THE MET AND PT ARE
EQUAL TO 2.0 BASED ON A STEADY TREND OVER THE PAST 24 HOURS. THE FT IS
BASED ON THE MET DUE TO BANDING FEATURES THAT WERE NOT CLEAR CUT WITH
INCONSISTENT CONVECTION AND UNCERTAINTY WITH THE EXACT LLCC POSITION IN
SATELLITE IMAGERY.

I. ADDL POSITIONS

30/1205Z 13.5N 111.6W GMI


...SAMBUCCI

[Yellow Evan]

TXPZ29 KNES 310021
TCSENP

A. 08E (HILDA)

B. 30/2330Z

C. 13.1N

D. 114.0W

E. THREE/GOES-W

F. T3.0/3.0

G. IR/EIR/VIS

H. REMARKS...5/10 WHITE BANDING AROUND THE LLCC MAKES THE DT EQUAL TO
3.0. THE MET AND PT AGREE AND ARE ALSO EQUAL TO 3.0 BASED ON A DEVELOPMENT
TREND OVER THE PAST 24 HOURS. A WELL DEFINED LLCC WAS OBSERVED TO THE
NORTHWEST OF PERSISTENT CONVECTION IN RECENT SATELLITE IMAGERY. THE FT
IS BASED ON THE DT.

I. ADDL POSITIONS

NIL


...SAMBUCCI

[cycloneye]

EP, 08, 2021073100, , BEST, 0, 129N, 1140W, 40, 1003, TS

[Sciencerocks]

[cycloneye]

Tropical Storm Hilda Discussion Number 2
NWS National Hurricane Center Miami FL EP082021
900 PM MDT Fri Jul 30 2021

Satellite imagery indicates that Hilda has gotten a little better
organized during the past several hours, with the low-level
center now near the eastern end of a long convective band that is
present in the southwestern semicircle. Satellite intensity
estimates are 35 kt from TAFB and 45 kt from SAB, and based on
these the initial intensity remains 40 kt. The storm is currently
in an environment of light northwesterly vertical wind shear with
the bulk of the outflow to the south.

Conditions generally appear favorable for strengthening during the
next 72 h or so, as Hilda is expected to be over warm sea surface
temperatures and in an environment of light to moderate shear.
Based on this, the first part of the intensity forecast is unchanged
from the previous forecast and calls for Hilda to become a
hurricane between 24 and 36 h and peak in intensity around 60 h.
After that, the forecast becomes less confident. The cyclone is
expected to move over decreasing sea surface temperatures after
72 h, and this should cause gradual weakening as indicated in the
official forecast. The official forecast for this period has been
nudged downward due to the forecast motion over cooler water.
However, the GFS and ECMWF models suggest the possibility that Hilda
will interact with other nearby systems - the GFS forecasting with
Tropical Depression Nine-E to the west and the ECMWF forecasting
interaction with a disturbance to the east. Should either of these
interactions occur, Hilda could weaken at a different rate than
currently forecast.

The initial motion is 290/13. Hilda is located on the south side
of a subtropical ridge, and if the storm does not interact with
other nearby weather systems a general west-northwestward motion
with a decrease in forward speed is expected through the forecast
period. The new forecast track is shifted a little north of the
previous track, and it lies just to the south of the various
consensus models. If Hilda does interact with either Tropical
Depression Nine-E or the disturbance to the east, it will lead to
erratic motion.


FORECAST POSITIONS AND MAX WINDS

INIT 31/0300Z 13.2N 114.6W 40 KT 45 MPH
12H 31/1200Z 13.5N 116.3W 50 KT 60 MPH
24H 01/0000Z 14.1N 118.4W 60 KT 70 MPH
36H 01/1200Z 14.7N 120.3W 70 KT 80 MPH
48H 02/0000Z 15.3N 122.0W 75 KT 85 MPH
60H 02/1200Z 15.8N 123.3W 75 KT 85 MPH
72H 03/0000Z 16.5N 124.8W 70 KT 80 MPH
96H 04/0000Z 18.0N 127.0W 60 KT 70 MPH
120H 05/0000Z 19.5N 131.0W 50 KT 60 MPH

$$
Forecaster Beven

[Sciencerocks]

[Kingarabian]

Very cold tops:

[Kingarabian]

TXPZ29 KNES 310605
TCSENP

A. 08E (HILDA)

B. 31/0530Z

C. 13.3N

D. 115.0W

E. THREE/GOES-W

F. T3.0/3.0

G. IR/EIR/SWIR

H. REMARKS...5/10 WHITE BANDING WITH PERSISTENT CONVECTION THAT WAS
OBSERVED AROUND THE LLCC MAKES THE DT EQUAL TO 3.0. THE MET AND PT AGREE
AND ARE ALSO EQUAL TO 3.0 BASED ON A RAPID DEVELOPMENT TREND OVER THE
PAST 24 HOURS. THE FT IS BASED ON THE DT.

I. ADDL POSITIONS

NIL


...SAMBUCCI

[cycloneye]

Tropical Storm Hilda Discussion Number 3
NWS National Hurricane Center Miami FL EP082021
200 AM PDT Sat Jul 31 2021

A prominent convective band now wraps about halfway around the
southeast to west side of Hilda's center, and another band is
taking shape to the north of the center. With the improved
organization, Dvorak estimates increased to a consensus T3.0/45 kt
from TAFB and SAB, and a 0520 UTC ASCAT-B pass confirmed that indeed
maximum winds are about 45 kt. This is being set as Hilda's
initial intensity, although it could be a little conservative since
objective ADT estimates have trended higher than that since 0600
UTC.

A mid-tropospheric ridge currently extends from northern Mexico
westward across the Baja California peninsula to about 120W and is
steering Hilda west-northwestward at 290/12 kt. Although this
ridge is expected to build westward and keep Hilda on a
west-northwestward course, potential interactions with Tropical
Depression Nine-E to the west and another low pressure area to the
east could cause the storm to slow down over the next 3 days and
oscillate a bit around that general heading. There is slightly more
spread among the track models than is typical, with the HWRF a
notable southern outlier and the GFS and HMON models having some of
the faster solutions due to greater interaction with T.D. Nine-E.
That being said, the overall track guidance has trended a little
slower and farther south on this cycle, and the updated NHC track
forecast has therefore been adjusted in that direction from the
previous forecast, lying close to the TVCE multi-model consensus but
not nearly as far south as the HCCA consensus aid.

Hilda is currently in a light-shear regime and over sea surface
temperatures of about 29 degrees Celsius, so continued
strengthening is anticipated in the short term with Hilda likely
to reach hurricane strength by tonight or early Sunday. However,
global models are suggesting that the shear may increase out of the
east during the next 24 hours, and then Hilda will be near cooler
waters in 2 to 3 days. Therefore, Hilda is likely to reach its
peak intensity in about 48 hours, and the NHC intensity forecast at
that time is near the upper end of the guidance suite. Hilda is
expected to move over even cooler waters after 48 hours, which
should cause a gradual weakening trend through the end of the
forecast period.


FORECAST POSITIONS AND MAX WINDS

INIT 31/0900Z 13.3N 115.7W 45 KT 50 MPH
12H 31/1800Z 13.6N 117.3W 55 KT 65 MPH
24H 01/0600Z 14.1N 119.1W 65 KT 75 MPH
36H 01/1800Z 14.6N 120.8W 70 KT 80 MPH
48H 02/0600Z 15.1N 122.3W 75 KT 85 MPH
60H 02/1800Z 15.7N 123.7W 70 KT 80 MPH
72H 03/0600Z 16.3N 124.8W 65 KT 75 MPH
96H 04/0600Z 17.8N 127.6W 55 KT 65 MPH
120H 05/0600Z 18.9N 131.5W 45 KT 50 MPH

$$
Forecaster Berg

[aspen]

Oh wow, this looks like it’s about to bomb out. Hilda might get strong enough to rip 9E apart with its outflow.

[Yellow Evan]

Despite the ULAC, SHIPS has shear rising quite a bit today so I’m skeptical of serious intensification.

[Yellow Evan]

TXPZ29 KNES 311155
TCSENP

A. 08E (HILDA)

B. 31/1130Z

C. 13.8N

D. 116.1W

E. THREE/GOES-W

F. T3.5/3.5

G. IR/EIR/SWIR

H. REMARKS...SYSTEM HAS DEVELOPED RAPIDLY OVER THE LAST 24 HOURS
RESULTING IN A MET OF 3.0. PT IS 3.5. 10/10 BANDING YIELDS A DT OF
3.5. FT IS BASED ON DT.

I. ADDL POSITIONS

NIL


...TURK

[aspen]

Despite the ULAC, SHIPS has shear rising quite a bit today so I’m skeptical of serious intensification.

Hopefully it becomes something impressive before then, because it’s probably going to kill 9E and 91E with its outflow no matter if it peaks as a strong TS or a major at this rate. It looks like it’s on track to become a hurricane by the 5pm advisory.