Tropical Cyclone Discussion
715 WTPZ43 KNHC 292048 TCDEP3 Tropical Storm Rachel Discussion Number 11 NWS National Hurricane Center Miami FL EP182026 300 PM CST Tue Sep 29 2026 There has been a wealth of data to parse through this afternoon with Rachel. On satellite imagery, Rachel is exhibiting a large convective burst with cloud tops below -85 C, though this burst is still centered a little south of the center fixes provided by the NOAA P-3 aircraft that conducted a research mission into the storm. The peak 700-mb flight level winds from the mission were 66 kt. In addition, there was a dropsonde launched in the radius of maximum wind on its east side that had 500 m average of 75 kt, which using a typical reduction factor yields 60 kt. Furthermore, there was a uncrewed aircraft system (UAS) that was launched in the same area in the boundary layer, finding 975-mb winds also up to 75 kt. An experimental reduction factor developed by CIRA indicated this value translates to a 10-meter sustained wind of 63 kt. All of the above data suggests that Rachel is nearly a hurricane, and the initial intensity is set at 60 kt this advisory. A 1620 UTC ASCAT-B pass, in addition to the aircraft data, were both useful to adjust the 34- and 50-kt radii this afternoon. Rachel continues to move off to the northwest, with aircraft fixes indicating a motion of 305 degrees at 12 kt. A mid-level ridge located over central Mexico is expected to steer the tropical cyclone in that same direction over the next 12-24 h. However, an upper-level cutoff low moving across the four corners region of the southwestern United States will soon erode this ridge, leading to a significant slowdown in Rachel's motion. After 48 h, another mid-level ridge begins to build in over California and Nevada behind this cutoff low as it ejects into the central Plains. The net effect of this synoptic pattern is Rachel should then turn more westward, but still at a slow forward motion. Some of the reliable track aids have made a southward shift in Rachel's track this afternoon, and the latest NHC track forecast has been shifted in that direction, blending the HFIP Corrected Consensus Approach (HCCA), the Google DeepMind ensemble mean (GDMI), and their new experimental model (WN3I). Shear analysis from UW-CIMSS indicates that the northeasterly shear that had been affecting Rachel is starting to decrease, and both the EC- and GFS-based SHIPS guidance show this lowering below 15 kt in 24 h. In addition, the latest forecast track brings Rachel initially to the north of the cool wake left behind by Polo, with nearby ocean drifters still showing sea-surface temperatures (SSTs) in the 29-30 C range still. Thus as the shear decreases, and assuming Rachel's core is becoming more vertically aligned, the short-term intensity has been raised and now shows a period of rapid intensification from 24-48 h, making it a 105 kt major hurricane at the end of that time frame. After that time, as Rachel turns westward, it will finally pass over Polo's cool wake, where another drifter in that vicinity showing SSTs much lower, in the 26-27 C range, and that combined with Rachel's slow motion will likely lead to weakening in 60-96 h. The latest NHC intensity forecast remains on the upper-end of the guidance, closest to HCCA through 48 h, but then falls back closer to the guidance mean in 72-120 h. Key Messages: 1. Although the core of Rachel is forecast to remain offshore of Mexico, tropical-storm-force winds are expected along a portion of the coast of southwestern Mexico in the Tropical Storm Warning area today or tonight. Tropical storm conditions are possible in the watch area tonight or on Wednesday. 2. Outer bands from Rachel will bring locally heavy rainfall to portions of coastal southwest Mexico through Thursday. This rainfall may produce life-threatening flooding and mudslides, especially in areas of steep terrain. 3. Large waves could produce life-threatening surf and rip current conditions along portions of the southwestern coast of Mexico during the next several days. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 16.0N 105.7W 60 KT 70 MPH 12H 30/0600Z 17.3N 107.0W 70 KT 80 MPH 24H 30/1800Z 18.2N 108.0W 85 KT 100 MPH 36H 01/0600Z 19.0N 108.9W 100 KT 115 MPH 48H 01/1800Z 19.4N 109.5W 105 KT 120 MPH 60H 02/0600Z 19.6N 110.3W 100 KT 115 MPH 72H 02/1800Z 19.8N 111.1W 90 KT 105 MPH 96H 03/1800Z 20.2N 112.9W 80 KT 90 MPH 120H 04/1800Z 20.5N 115.0W 85 KT 100 MPH