EPAC: HILARY - Post-Tropical - Discussion

[cycloneye]

Tropical Storm Hilary Discussion Number 1
NWS National Hurricane Center Miami FL EP092023
1000 AM CDT Wed Aug 16 2023

The disturbance south of the southern coast of Mexico has increased
in organization this morning. Satellite imagery indicates that it
has a well-defined circulation, with convective banding features
that are becoming better defined. Subjective Dvorak estimates from
TAFB and SAB are at T1.5 and T2.0, respectively, however the
T-number from TAFB was constrained. First-light visible satellite
imagery confirms the organizing trend and, based on the improved
appearance of the cloud pattern over the past few hours, the system
is being upgraded to Tropical Storm Hilary.

Hilary is moving west-northwestward at 12 kt. A building ridge over
the United States and a trough off the coast of California are the
main steering features affecting the storm. The tropical cyclone
is forecast to make a gradual turn to the northwest in 24 hours,
and then turn more northward between the trough and the western
periphery of the ridge by day 3. Global model guidance is
relatively well-clustered for the first 3 days, with some larger
cross-track differences by day 4 and beyond. The official track
forecast is closest to the simple and corrected consensus aids.

The environmental and oceanic conditions appear ripe for further
strengthening. Sea surface temperatures are at or near a warm 30
degrees C through 72 h, vertical wind shear is expected to be
weak, and the near-storm relative humidities are moist.
Statistical intensity guidance show high probabilities of rapid
intensification in the next couple of days. Therefore, the NHC
intensity prediction explicitly shows rapid intensification in the
first 24 hours and Hilary is expected to become a hurricane on
Thursday. However, the system is broad and it could take slightly
longer to consolidate and strengthen. The storm is likely to reach
its peak intensity in 60-72 hours. By day 4, the vertical wind
shear is forecast to increase and the track forecast moves Hilary
over waters cooler than 26 degree C. Convection will likely
collapse and the system is expected to become post-tropical by day
5.

It is important to remind users to not focus on the exact forecast
track and intensity of Hilary, especially in the latter parts of
the forecast period.

KEY MESSAGES:

1. Hilary has the potential to bring impacts to the Baja California
Peninsula and portions of the southwestern United States this
weekend. Although it is too soon to determine the location and
magnitude of rainfall and wind impacts, interests in these areas
should monitor the progress of Hilary and updates to the forecast.

2. Large swells from Hilary will spread northward along the coast
of southwestern Mexico and the Baja California Peninsula during the
next days.

FORECAST POSITIONS AND MAX WINDS

INIT 16/1500Z 12.4N 102.6W 35 KT 40 MPH
12H 17/0000Z 13.1N 104.3W 50 KT 60 MPH
24H 17/1200Z 14.1N 106.5W 65 KT 75 MPH
36H 18/0000Z 15.4N 108.7W 75 KT 85 MPH
48H 18/1200Z 16.7N 110.7W 90 KT 105 MPH
60H 19/0000Z 18.5N 112.3W 105 KT 120 MPH
72H 19/1200Z 20.4N 113.6W 105 KT 120 MPH
96H 20/1200Z 25.7N 114.8W 80 KT 90 MPH
120H 21/1200Z 31.5N 116.8W 50 KT 60 MPH...POST-TROPICAL

$$
Forecaster Bucci/Camposano

[Teban54]

Is a 105 kt forecast on the first advisory a record in the EPac? I think the current record for the Atlantic is 100 kt on the first advisory, held by Tomas 2010 and Sam 2021.

[wxman57]

SSTs are about 70 degrees off the northern Baja Peninsula. That's pretty cool. Could be some rain for CA, though.

[wxman57]

Is a 105 kt forecast on the first advisory a record in the EPac? I think the current record for the Atlantic is 100 kt on the first advisory, held by Tomas 2010 and Sam 2021.

It means that the NHC should have started advisories earlier.

[cycloneye]

Is a 105 kt forecast on the first advisory a record in the EPac? I think the current record for the Atlantic is 100 kt on the first advisory, held by Tomas 2010 and Sam 2021.

It means that the NHC should have started advisories earlier.

Agree. Since yesterday evening it was already organizing.

[Sciencerocks]

 https://twitter.com/zoom_earth/status/1691834541026005035

[aspen]

I think Hilary as a shot at Cat 5 intensity. SSTs, its moisture envelope, and UL outflow will be incredibly favorable for the next 2-3 days. The only limiting factor is just how fast Hilary can tighten up. Adrian was a storm that started out as a broad disturbance, but tightened up remarkably well and possibly became a major. If Hilary performs similarly, 130+ kt is on the table.

[cycloneye]

[wxman57]

Is a 105 kt forecast on the first advisory a record in the EPac? I think the current record for the Atlantic is 100 kt on the first advisory, held by Tomas 2010 and Sam 2021.

It means that the NHC should have started advisories earlier.

Agree. Since yesterday evening it was already organizing.

Perhaps they were considering the repercussions of aiming a TS at southern CA? I know that we were concerned about that when we started advisories at 7am yesterday. Lots of conference calls this weekend, most likely. They slowed the storm way down beyond Sunday, keeping it near northern Baja at 50 kts post-tropical. Kind of a "To be continued..." track.

[Ntxw]

I think Hilary as a shot at Cat 5 intensity. SSTs, its moisture envelope, and UL outflow will be incredibly favorable for the next 2-3 days. The only limiting factor is just how fast Hilary can tighten up. Adrian was a storm that started out as a broad disturbance, but tightened up remarkably well and possibly became a major. If Hilary performs similarly, 130+ kt is on the table.

This has the deep convection of the bigger ones in the region. I remember 2017's version of Hilary that was expected to be a big one by models but flopped. However that was mid July with slightly cooler SSTs and it took forever to get a core together.

[cycloneye]

We have recon for next Friday.

https://www.storm2k.org/phpbb2/viewtopi ... 2#p3032962

[Ntxw]

We have recon for next Friday.

https://www.storm2k.org/phpbb2/viewtopi ... 2#p3032962

Friday should be peak day.

[cycloneye]

 https://twitter.com/MikeAdcockWx/status/1691852369175216254

[Ntxw]

[Kingarabian]

It means that the NHC should have started advisories earlier.

Agree. Since yesterday evening it was already organizing.

Perhaps they were considering the repercussions of aiming a TS at southern CA? I know that we were concerned about that when we started advisories at 7am yesterday. Lots of conference calls this weekend, most likely. They slowed the storm way down beyond Sunday, keeping it near northern Baja at 50 kts post-tropical. Kind of a "To be continued..." track.

Yeah SoCal looks like a possibility.

[cycloneye]

EP, 09, 2023081618, , BEST, 0, 134N, 1031W, 35, 1002, TS

[cycloneye]

Long twit.

 https://twitter.com/VortixWx/status/1691890538461450720

1. SSTs will become unsupportive for a tropical cyclone to survive in. The isotherm is below 26C, which in most cases won’t help TCs like Hilary at all. And the storms that survive tend to be supported by the upper levels of the atmosphere which are subtropical systems and Hilary isn’t one of them. Given the -PMM (Pacific Meridional Mode) being in the negative state, this is definitely against Hilary’s favor being that the waters are that cold offshore of the Baja California Peninsula.

2. Increased vertical wind shear. Remember, tropical cyclones are stacked like a Jenga Tower. If you have a change of wind speed with height and/or direction, it will not go well for it. In Hilary’s case, it’s a weird since there’s a negative tilted trough in the NE Pacific offshore of CA & a ridge in the Rockies. This should provide divergence aloft & spread Hilary’s outflow aloft. Normally, that would help a TC but remember, the SSTs are mid and it will be too much backside shear for Hilary which would mean it will adversely affect it. However, it would help it weaken slowly but it will soon become extratropical.

3. The trajectory matters. It’s important to remember that the cone is specifically designed to show where the center of a TC could be. So it could sway left or the right side of the cone & the cone could definitely change. The Super-ensemble chart shows the split between staying offshore & trekking through land & even then, it could hit #BajaCalifornia & just go to CA from there, which won’t mean a landfall because a landfall is when a TC moves from sea to land.

So that means that Hilary is unlikely to reach hurricane status at landfall in California.

However, we must urge y’all that just because Hilary doesn’t do that, doesn’t mean that there will be no impacts to there. Flooding & some gusty winds are definitely a possibility for the state or generally speaking, the SW #USA. It’s best to keep on monitoring for updates on Hilary from places like the NHC or your local weather office.

[cycloneye]

* EAST PACIFIC 2023 SHIPS INTENSITY FORECAST *
* IR SAT DATA AVAILABLE, OHC AVAILABLE *
* HILARY EP092023 08/16/23 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 35 41 50 60 71 93 109 120 119 107 90 67 44 32 36 N/A N/A
V (KT) LAND 35 41 50 60 71 93 109 120 119 107 90 59 45 32 29 N/A N/A
V (KT) LGEM 35 38 42 48 57 80 111 130 122 94 63 40 35 28 27 N/A N/A
Storm Type TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP EXTP EXTP N/A N/A

SHEAR (KT) 10 7 8 4 1 7 6 5 4 8 9 11 12 11 10 N/A N/A
SHEAR ADJ (KT) -4 -6 -3 -4 -3 -6 -5 -1 4 9 4 5 1 -3 0 N/A N/A
SHEAR DIR 24 21 323 285 238 44 8 116 117 154 176 193 198 208 215 N/A N/A
SST (C) 30.4 30.3 30.2 30.3 30.1 30.2 30.2 29.1 27.3 25.8 22.5 23.3 20.3 19.1 15.6 N/A N/A
POT. INT. (KT) 170 169 168 169 167 168 168 156 138 123 89 97 65 60 60 N/A N/A
200 MB T (C) -51.1 -50.7 -51.1 -51.2 -50.7 -50.5 -49.7 -49.6 -49.0 -48.3 -48.1 -47.5 -47.3 -48.4 -49.7 N/A N/A
200 MB VXT (C) 0.5 0.5 0.6 0.7 0.8 0.8 0.9 1.2 1.4 1.5 1.6 1.3 1.5 0.8 0.5 N/A N/A
TH_E DEV (C) 6 6 6 6 7 6 6 4 3 3 2 2 3 2 3 N/A N/A
700-500 MB RH 84 85 85 85 84 82 80 76 72 59 58 50 43 38 38 N/A N/A
MODEL VTX (KT) 26 28 31 33 36 42 46 51 52 47 40 27 13 5 3 LOST LOST
850 MB ENV VOR 68 69 59 64 75 87 112 113 118 107 124 87 65 23 -11 N/A N/A
200 MB DIV 133 153 161 133 162 192 151 151 144 70 51 16 37 13 34 N/A N/A
700-850 TADV -10 -7 -7 -7 -6 -6 2 0 2 17 10 -5 18 19 20 N/A N/A
LAND (KM) 488 506 509 504 504 580 547 424 368 244 30 -28 14 -107 -221 N/A N/A
LAT (DEG N) 13.4 13.8 14.2 14.9 15.5 16.7 18.2 20.2 22.0 24.7 28.1 31.0 33.2 xx.x xx.x N/A N/A
LONG(DEG W) 103.1 104.3 105.4 106.5 107.5 109.7 111.5 112.9 114.0 114.6 115.0 115.9 117.6 xxx.x xxx.x N/A N/A
STM SPEED (KT) 13 12 12 12 12 12 11 11 12 15 16 14 12 9 7 N/A N/A
HEAT CONTENT 56 50 41 39 30 33 27 14 2 0 0 0 0 0 0 N/A N/A

FORECAST TRACK FROM OFCI INITIAL HEADING/SPEED (DEG/KT):300/ 13 CX,CY: -10/ 7
T-12 MAX WIND: 35 PRESSURE OF STEERING LEVEL (MB): 651 (MEAN=588)
GOES IR BRIGHTNESS TEMP. STD DEV. 50-200 KM RAD: 13.2 (MEAN=14.5)
% GOES IR PIXELS WITH T < -20 C 50-200 KM RAD: 96.0 (MEAN=65.0)
PRELIM RI PROB (DV .GE. 35 KT IN 36 HR): 82.3

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. 1. 1. 1. 1. 2. 2. 1. 1. -0. -1. -1. -2. -3. 0. 0.
SST POTENTIAL 0. 0. 1. 2. 7. 13. 18. 22. 22. 21. 20. 16. 13. 19. 0. 0.
VERTICAL SHEAR MAG 0. 1. 2. 3. 5. 6. 8. 9. 10. 12. 13. 14. 14. 12. 0. 0.
VERTICAL SHEAR ADJ 0. 1. 1. 2. 3. 4. 4. 2. 1. 1. 0. 0. 0. 0. 0. 0.
VERTICAL SHEAR DIR 0. 0. -0. -1. -0. -0. -0. -1. -1. -1. -0. -0. 0. 0. 0. 0.
PERSISTENCE -0. -0. -0. -1. -1. -1. -0. -0. -0. -0. -0. -0. -0. -0. 0. 0.
200/250 MB TEMP. -0. -0. -1. -1. -2. -2. -1. -1. -0. 1. 3. 5. 7. 7. 0. 0.
THETA_E EXCESS -0. -0. -0. -0. 0. -0. -0. -1. -2. -3. -3. -4. -4. -4. 0. 0.
700-500 MB RH 0. 0. 1. 1. 2. 2. 2. 2. 2. 2. 1. 1. 0. 0. 0. 0.
MODEL VTX TENDENCY 1. 3. 5. 8. 12. 20. 32. 36. 29. 18. 2. -15. -23. -22. 0. 0.
850 MB ENV VORTICITY 0. 0. 0. 0. 0. 0. -0. -0. -1. -1. -1. -1. -1. -1. 0. 0.
200 MB DIVERGENCE 0. 1. 1. 1. 2. 3. 5. 8. 8. 8. 6. 4. 1. -0. 0. 0.
850-700 T ADVEC 0. 0. 0. 0. 0. 0. 0. 0. 0. -0. -0. 0. 0. 1. 0. 0.
ZONAL STORM MOTION 0. -0. -0. -0. 0. 0. 0. -0. -0. -0. -0. -0. -0. -1. 0. 0.
STEERING LEVEL PRES 0. 0. 0. 0. 1. 1. 1. 1. 1. 2. 2. 2. 2. 1. 0. 0.
DAYS FROM CLIM. PEAK 0. 0. 0. 0. 1. 1. 1. 1. 2. 2. 2. 3. 3. 4. 0. 0.
GOES PREDICTORS 1. 2. 2. 2. 2. 2. 2. 2. 2. 2. 3. 3. 3. 2. 0. 0.
OCEAN HEAT CONTENT -0. -0. -0. -0. -0. 0. 1. 0. -0. -0. -0. -0. -0. 0. 0. 0.
RI POTENTIAL 2. 6. 11. 16. 26. 23. 13. 3. -3. -9. -14. -16. -16. -16. 0. 0.
--------------------------------------------------------------------------------------------
TOTAL CHANGE 6. 15. 25. 36. 58. 74. 85. 84. 72. 55. 32. 9. -3. 1. 0. 0.

CURRENT MAX WIND (KT): 35. LAT, LON: 13.4 103.1

** 2023 E. PACIFIC RI INDEX EP092023 HILARY 08/16/23 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) : 133.7 36.9 to 148.5 0.87 23.7
12 HR PERSISTENCE (KT) : 0.0 -22.0 to 44.0 0.33 7.9
MULTI-LAYER SHEAR (KT) : 12.0 30.9 to 7.7 0.82 15.2
BL DRY-AIR FLUX (W/M2) : -10.6 816.2 to -81.4 0.92 -19.4
D200 (10**7s-1) : 148.4 -33.0 to 159.5 0.94 15.4
MAXIMUM WIND (KT) : 35.0 22.5 to 132.0 0.36 5.7
STD DEV OF IR BR TEMP : 13.2 37.8 to 2.1 0.69 9.0
HEAT CONTENT (KJ/CM2) : 43.2 2.7 to 103.4 0.40 3.2
%area of TPW <45 mm upshear : 0.0 49.8 to 0.0 1.00 5.0
2nd PC OF IR BR TEMP : -0.5 2.2 to -2.3 0.60 0.2

SHIPS Prob RI for 20kt/ 12hr RI threshold= 16% is 2.6 times climatological mean ( 6.3%)
SHIPS Prob RI for 25kt/ 24hr RI threshold= 78% is 6.2 times climatological mean (12.5%)
SHIPS Prob RI for 30kt/ 24hr RI threshold= 66% is 7.6 times climatological mean ( 8.6%)
SHIPS Prob RI for 35kt/ 24hr RI threshold= 48% is 7.7 times climatological mean ( 6.2%)
SHIPS Prob RI for 40kt/ 24hr RI threshold= 41% is 9.8 times climatological mean ( 4.2%)
SHIPS Prob RI for 45kt/ 36hr RI threshold= 91% is 13.6 times climatological mean ( 6.7%)
SHIPS Prob RI for 55kt/ 48hr RI threshold= 99% is 16.8 times climatological mean ( 5.9%)
SHIPS Prob RI for 65kt/ 72hr RI threshold= 75% is 16.0 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: 16.3% 77.9% 65.8% 47.9% 41.0% 91.4% 99.2% 75.1%
Logistic: 10.2% 68.2% 46.6% 32.6% 23.7% 63.5% 80.8% 7.8%
Bayesian: 3.0% 35.3% 38.6% 13.6% 3.2% 36.4% 20.3% 14.0%
Consensus: 9.8% 60.4% 50.3% 31.4% 22.6% 63.8% 66.8% 32.3%
DTOPS: 18.0% 60.0% 42.0% 30.0% 15.0% 67.0% 72.0% 61.0%

## ANNULAR HURRICANE INDEX (AHI) EP092023 HILARY 08/16/23 18 UTC ##
## STORM NOT ANNULAR, SCREENING STEP FAILED, NPASS=3 NFAIL=4 ##
## AHI= 0 (AHI OF 100 IS BEST FIT TO ANN. STRUC., 1 IS MARGINAL, 0 IS NOT ANNULAR) ##

[Zonacane]

SSTs are about 70 degrees off the northern Baja Peninsula. That's pretty cool. Could be some rain for CA, though.

How much rain should Tucson and southern AZ see from Hillary?

[cycloneye]

Tropical Storm Hilary Discussion Number 2
NWS National Hurricane Center Miami FL EP092023
400 PM CDT Wed Aug 16 2023

Hilary has not changed much this afternoon. A large burst of
convection, with cloud top temperatures colder than -85 degrees C,
continues to obscure the low-level circulation and some outflow has
developed on the southern semicircle of the storm. Subjective and
objective satellite intensity estimates range from 30 to 43 kt and
the initial intensity is remains at 35 kt.

The storm is moving to the west-northwest at 13 kt. Hilary is
forecast to gradually turn, first to the northwest by day 2 and
then to the north-northwest by day 3 with the same general forward
motion. This is likely driven by a building ridge over the United
States and a trough off the coast of California. The short-term
track prediction has shifted to the right of the previous forecast,
largely due to an adjustment in the rather uncertain initial
position. It is closest to the simple consensus aid, TVCE.

Strengthening is still expected due to the conducive atmospheric
conditions and warm sea surface temperatures. Hilary is forecast to
be in an area of weak vertical wind shear through 72-96 hours and
remain over warm waters through 72 hours. Therefore, steady to
rapid intensification is anticipated and the official forecast
shows Hilary becoming a hurricane in 24 hours. However, the system
is broad and it could take slightly longer to initially consolidate
and strengthen. Beyond day 3, Hilary is forecast to cross over a
gradient of cooling ocean waters which should induce a weakening
trend. The system is still expected to be post-tropical by the end
of the forecast period.

It is important to remind users to not focus on the exact forecast
track and intensity of Hilary, especially in the latter parts of the
forecast period. Due to the nearly parallel angle of approach to
the Baja California peninsula, small changes in the cross track
position may result in large changes to when and where the system
ultimately approaches the coast. Regardless, wind and rainfall
impacts are likely to extend far from the center of Hilary.

KEY MESSAGES:

1. Hilary has the potential to bring impacts to the Baja California
Peninsula and portions of the southwestern United States this
weekend. Although it is too soon to determine the location and
magnitude of rainfall and wind impacts, interests in these areas
should monitor the progress of Hilary and updates to the forecast.

2. Large swells from Hilary will spread northward along the coast
of southwestern Mexico and the Baja California Peninsula during the
next days.


FORECAST POSITIONS AND MAX WINDS

INIT 16/2100Z 13.7N 103.7W 35 KT 40 MPH
12H 17/0600Z 14.5N 105.4W 50 KT 60 MPH
24H 17/1800Z 15.6N 107.6W 65 KT 75 MPH
36H 18/0600Z 16.8N 109.6W 75 KT 85 MPH
48H 18/1800Z 18.2N 111.3W 90 KT 105 MPH
60H 19/0600Z 20.0N 112.8W 105 KT 120 MPH
72H 19/1800Z 22.3N 113.7W 105 KT 120 MPH
96H 20/1800Z 27.8N 115.2W 70 KT 80 MPH
120H 21/1800Z 34.3N 118.3W 40 KT 45 MPH...POST-TROP/INLAND

$$
Forecaster Bucci