Tropical Cyclone Discussion
Issued by NWS
Issued by NWS
479 WTPZ42 KNHC 030242 TCDEP2 Tropical Storm Lorena Discussion Number 5 NWS National Hurricane Center Miami FL EP122025 800 PM MST Tue Sep 02 2025 A pair of AMSR2 and GMI microwave passes from several hours ago revealed that Lorena`s structure has improved significantly through the day, with the 37-GHZ channel in particular showing a well-defined cyan ring. The center is embedded beneath a Central Dense Overcast, and Dvorak intensity estimates from TAFB and SAB are a consensus T3.5/55 kt. This is also supported by some of the UW-CIMSS objective numbers, and the initial intensity is therefore set--possibly conservatively given the structure--at 55 kt. Lorena has a low-level structure and small size that would make it a prime suspect for rapid intensification, especially since it will be in an environment of low shear and over warm ocean temperatures for the next 36 hours. In fact, the SHIPS Rapid Intensification (RI) index now shows a 3 in 4 chance of a 30-kt increase in Lorena`s winds over the next 24 hours. The NHC intensity forecast therefore explicitly shows RI during the next day or so and most closely follows the SHIPS and LGEM models, which are the highest guidance, during that time. After 36 hours, increasing shear and colder water temperatures are expected lead to weakening, which itself could be rapid due to Lorena`s small size. Although there is significant uncertainty on where Lorena will end up in 4-5 days (see discussion below), the cyclone will likely not exist anymore by day 5, and that is when dissipation is shown in the forecast. Lorena continues to move northwestward, or 315/12 kt. The first 36 hours or so of the track forecast are fairly straightforward, with a slower northwestward motion expected while the cyclone moves around the western periphery of a mid-level high centered over Mexico. Things are trickier after 36 hours. Lorena will be moving through a weakness in the subtropical ridge, but how much northward progress it makes will depend on how long it remains strong. A minority of models, particularly the GFS, keep a stronger Lorena moving northeastward across the Baja California peninsula toward Sonora. However, moderate to strong southwesterly shear is likely to set in over Lorena in 48-72 hours, and a good chunk of the other models, including many of the GEFS ensemble members, keep a weakening Lorena offshore the west coast of the Baja California peninsula with landfall never occurring. This new NHC forecast blends the previous official forecast with the latest HCCA, Florida State Superensemble, and GEFS ensemble mean, showing a slower motion on day 4 and 5, and introducing the possibility that Lorena doesn`t reach mainland Mexico as a tropical cyclone. Key Messages: 1. Heavy rainfall associated with Tropical Storm Lorena will begin to affect Baja California Sur on Wednesday, southwestern Sonora by Thursday, and contribute to heavy rainfall concerns across Arizona late Wednesday through Friday. This will increase the risk of life-threatening flash floods and mudslides across Mexico, especially in areas of higher terrain. Isolated to scattered instances of flash flooding are possible across Arizona through Friday. 2. Although rapid intensification is possible through Wednesday while Lorena is offshore, the storm is expected to weaken while it approaches the Baja California peninsula on Thursday and Friday. Regardless, tropical storm conditions are possible through Thursday along portions of the west coast of Baja California Sur. Interests in Baja California Sur should closely monitor the latest forecast updates. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 20.2N 109.7W 55 KT 65 MPH 12H 03/1200Z 21.2N 111.1W 70 KT 80 MPH 24H 04/0000Z 22.3N 112.6W 85 KT 100 MPH 36H 04/1200Z 23.4N 113.5W 90 KT 105 MPH 48H 05/0000Z 24.6N 113.9W 75 KT 85 MPH 60H 05/1200Z 25.6N 113.8W 55 KT 65 MPH 72H 06/0000Z 26.6N 113.3W 40 KT 45 MPH 96H 07/0000Z 28.1N 112.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 08/0000Z...DISSIPATED $$ Forecaster Berg