Issued at 500 AM AST Mon Oct 13 2025
616 WTNT42 KNHC 130857 TCDAT2 Tropical Storm Lorenzo Discussion Number 1 NWS National Hurricane Center Miami FL AL122025 500 AM AST Mon Oct 13 2025 The area of low pressure we have been monitoring over the last day or two (AL97) has become better organized this morning. After spending most of yesterday as an exposed low-level swirl, tonight a large burst of deep convection with cloud top temperatures below -80C has formed near and just east of the center. An earlier ASCAT-C pass clipped the eastern side of the system, showing that it was already producing tropical-storm-force winds, with a peak derived wind of 36 kt. A pair of AMSR2 and GMI microwave passes at 04-06 UTC near the system also showed the improved structural organization under the cirrus. The subjective 06 UTC Dvorak fix from TAFB was T2.5/35 kt, and the satellite presentation has only grown more impressive since that time, with the convective cloud tops taking a distinct comma shape pattern. Thus, advisories are being initiated on Tropical Storm Lorenzo this morning, with an initial intensity of 40 kt, assuming a little undersampling from the earlier scatterometer wind data. The initial motion is a somewhat uncertain 305/15 kt, a little slower than the center being tracked earlier, potentially due to the large convective burst tugging at the center. This general northwestward motion with some additional slowdown is anticipated today as Lorenzo approaches a weakness in the subtropical ridging produced by an upper-level trough in the path of the tropical cyclone. This trough is expected to fracture and shift to the southwest of the system, and Lorenzo should turn northward between this feature and the eroded mid-level ridge centered over the Cabo Verde Islands. Ultimately, this ridge should result in the cyclone recurving to the northeast around it, as it comes under influence of broad-scale mid-latitude westerly flow. The initial NHC track forecast is in pretty good agreement with a fairly tightly clustered track guidance envelope, and is roughly a blend of the HCCA and Google DeepMind guidance this cycle, a little east of the overall track envelope. While Lorenzo's structure on satellite imagery has improved, it is still currently experiencing about 25-30 kt of southwesterly vertical wind shear. However, both the GFS and ECMWF-based SHIPS guidance suggests this shear will soon lessen to less than 10 kts in 24-48 hours. Ordinarily this would lead to strengthening given the sufficently warm 27-28 C ocean temperatures, but at the same time, environmental mid-level relatively humidity is also expected to dry substantially as the storm interacts with the upper-level trough ahead of it. This trough could also still produce some residual mid-level shear undercutting the outflow layer. The overall guidance is not that enthusiastic about Lorenzo's intensity prospects, but it is worth noting there is quite a bit of spread in both the ECMWF and Google DeepMind ensemble members, ranging from a very weak tropical cyclone to a category 2 hurricane. The initial NHC intensity forecast will try to split the difference, showing little change in strength in the short-term while the shear remains high, and then just gradual intensification afterwards. This is higher than the majority of the hurricane-regional model guidance this cycle, but under the Google DeepMind ensemble mean and HWRF model. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 14.2N 40.3W 40 KT 45 MPH 12H 13/1800Z 15.0N 41.7W 40 KT 45 MPH 24H 14/0600Z 16.2N 43.4W 40 KT 45 MPH 36H 14/1800Z 18.0N 44.4W 45 KT 50 MPH 48H 15/0600Z 20.1N 44.7W 50 KT 60 MPH 60H 15/1800Z 22.4N 44.2W 55 KT 65 MPH 72H 16/0600Z 25.1N 42.6W 60 KT 70 MPH 96H 17/0600Z 30.9N 36.9W 55 KT 65 MPH 120H 18/0600Z 33.2N 29.6W 45 KT 50 MPH $$ Forecaster Papin
NHC Atlantic
